[feature] support processing of (many) more media types (#3090)

* initial work replacing our media decoding / encoding pipeline with ffprobe + ffmpeg

* specify the video codec to use when generating static image from emoji

* update go-storage library (fixes incompatibility after updating go-iotools)

* maintain image aspect ratio when generating a thumbnail for it

* update readme to show go-ffmpreg

* fix a bunch of media tests, move filesize checking to callers of media manager for more flexibility

* remove extra debug from error message

* fix up incorrect function signatures

* update PutFile to just use regular file copy, as changes are file is on separate partition

* fix remaining tests, remove some unneeded tests now we're working with ffmpeg/ffprobe

* update more tests, add more code comments

* add utilities to generate processed emoji / media outputs

* fix remaining tests

* add test for opus media file, add license header to utility cmds

* limit the number of concurrently available ffmpeg / ffprobe instances

* reduce number of instances

* further reduce number of instances

* fix envparsing test with configuration variables

* update docs and configuration with new media-{local,remote}-max-size variables

1 files changed, 0 insertions, 88 deletions

diff --git a/vendor/github.com/golang/geo/s2/nthderivative.go b/vendor/github.com/golang/geo/s2/nthderivative.go
deleted file mode 100644
index 73445d6c9..000000000
--- a/vendor/github.com/golang/geo/s2/nthderivative.go
+++ /dev/null
@@ -1,88 +0,0 @@
-// Copyright 2017 Google Inc. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package s2
-
-// nthDerivativeCoder provides Nth Derivative Coding.
-//   (In signal processing disciplines, this is known as N-th Delta Coding.)
-//
-// Good for varint coding integer sequences with polynomial trends.
-//
-// Instead of coding a sequence of values directly, code its nth-order discrete
-// derivative.  Overflow in integer addition and subtraction makes this a
-// lossless transform.
-//
-//                                       constant     linear      quadratic
-//                                        trend       trend         trend
-//                                      /        \  /        \  /           \_
-// input                               |0  0  0  0  1  2  3  4  9  16  25  36
-// 0th derivative(identity)            |0  0  0  0  1  2  3  4  9  16  25  36
-// 1st derivative(delta coding)        |   0  0  0  1  1  1  1  5   7   9  11
-// 2nd derivative(linear prediction)   |      0  0  1  0  0  0  4   2   2   2
-//                                      -------------------------------------
-//                                      0  1  2  3  4  5  6  7  8   9  10  11
-//                                                  n in sequence
-//
-// Higher-order codings can break even or be detrimental on other sequences.
-//
-//                                           random            oscillating
-//                                      /               \  /                  \_
-// input                               |5  9  6  1   8  8  2 -2   4  -4   6  -6
-// 0th derivative(identity)            |5  9  6  1   8  8  2 -2   4  -4   6  -6
-// 1st derivative(delta coding)        |   4 -3 -5   7  0 -6 -4   6  -8  10 -12
-// 2nd derivative(linear prediction)   |     -7 -2  12 -7 -6  2  10 -14  18 -22
-//                                      ---------------------------------------
-//                                      0  1  2  3  4   5  6  7   8   9  10  11
-//                                                  n in sequence
-//
-// Note that the nth derivative isn't available until sequence item n.  Earlier
-// values are coded at lower order.  For the above table, read 5 4 -7 -2 12 ...
-type nthDerivativeCoder struct {
-	n, m   int
-	memory [10]int32
-}
-
-// newNthDerivativeCoder returns a new coder, where n is the derivative order of the encoder (the N in NthDerivative).
-// n must be within [0,10].
-func newNthDerivativeCoder(n int) *nthDerivativeCoder {
-	c := &nthDerivativeCoder{n: n}
-	if n < 0 || n > len(c.memory) {
-		panic("unsupported n. Must be within [0,10].")
-	}
-	return c
-}
-
-func (c *nthDerivativeCoder) encode(k int32) int32 {
-	for i := 0; i < c.m; i++ {
-		delta := k - c.memory[i]
-		c.memory[i] = k
-		k = delta
-	}
-	if c.m < c.n {
-		c.memory[c.m] = k
-		c.m++
-	}
-	return k
-}
-
-func (c *nthDerivativeCoder) decode(k int32) int32 {
-	if c.m < c.n {
-		c.m++
-	}
-	for i := c.m - 1; i >= 0; i-- {
-		c.memory[i] += k
-		k = c.memory[i]
-	}
-	return k
-}