fpdf: handle 16-bit depth PNG files

Fixes #49.

Signed-off-by: Sebastien Binet <[email protected]>

fpdf: allow to set global document language

The Document Catalog of a PDF allows to "specify the natural
language for all text in the document" [1]. This is important to make
PDFs accessible.

This change allows to set the Lang entry in the document catalog.

[1] PDF 1.7, section 7.7.2, page 74
https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/PDF32000_2008.pdf

pdf: set the default barcode quality to 100

all: properly acknowledge original fork

This CL properly acknowledge the work of Kurt Jung.

Fixes #17.

ci: add Go-1.17

all: retract v1.4.3+v1.4.2

Signed-off-by: Sebastien Binet <[email protected]>

all: drop support for pre-Go-1.16

fpdf: introduce buffer pool for (de)flating buffers

```
  name              old time/op    new time/op    delta
  ParsePNG_rgb-8      22.8ms ± 1%    16.0ms ± 3%  -29.81%  (p=0.000 n=25+30)
  ParsePNG_gray-8      660µs ± 3%     624µs ± 4%   -5.54%  (p=0.000 n=28+30)
  ParsePNG_small-8    2.49µs ± 2%    2.12µs ± 3%  -14.83%  (p=0.000 n=30+30)
  ParseJPG-8          36.3µs ± 4%    36.8µs ± 5%     ~     (p=0.070 n=30+30)
  ParseGIF-8           410µs ± 3%     409µs ± 4%     ~     (p=0.562 n=30+29)

  name              old alloc/op   new alloc/op   delta
  ParsePNG_rgb-8      26.4MB ± 0%     4.2MB ±10%  -84.04%  (p=0.000 n=29+30)
  ParsePNG_gray-8     2.56MB ± 0%    2.49MB ± 0%   -2.73%  (p=0.000 n=30+30)
  ParsePNG_small-8    8.96kB ± 0%    9.84kB ± 0%   +9.73%  (p=0.000 n=30+30)
  ParseJPG-8           274kB ± 0%     274kB ± 0%   -0.00%  (p=0.002 n=30+30)
  ParseGIF-8           897kB ± 0%     898kB ± 0%   +0.10%  (p=0.000 n=30+30)

  name              old allocs/op  new allocs/op  delta
  ParsePNG_rgb-8         400 ± 0%       292 ± 0%  -27.00%  (p=0.000 n=30+28)
  ParsePNG_gray-8        164 ± 0%       114 ± 0%  -30.49%  (p=0.000 n=30+30)
  ParsePNG_small-8      35.0 ± 0%      10.0 ± 0%  -71.43%  (p=0.000 n=30+30)
  ParseJPG-8            12.0 ± 0%      12.0 ± 0%     ~     (all equal)
  ParseGIF-8             214 ± 0%       191 ± 0%  -10.75%  (p=0.000 n=30+30)
```

all: use raw endpoint from github

all: optimize rgbColorValue

This CL introduces a per-document buffer to build color strings.

```
name        old time/op    new time/op    delta
RGB_grg-8      808ns ± 0%     576ns ± 0%  -28.66%  (p=0.000 n=17+18)
RGB_gray-8     779ns ± 0%     584ns ± 0%  -25.01%  (p=0.000 n=18+18)
RGB_full-8     746ns ± 1%     568ns ± 1%  -23.89%  (p=0.000 n=19+19)

name        old alloc/op   new alloc/op   delta
RGB_grg-8      64.0B ± 0%     24.0B ± 0%  -62.50%  (p=0.000 n=20+20)
RGB_gray-8     48.0B ± 0%     24.0B ± 0%  -50.00%  (p=0.000 n=20+20)
RGB_full-8     48.0B ± 0%     24.0B ± 0%  -50.00%  (p=0.000 n=20+20)

name        old allocs/op  new allocs/op  delta
RGB_grg-8       5.00 ± 0%      1.00 ± 0%  -80.00%  (p=0.000 n=20+20)
RGB_gray-8      4.00 ± 0%      1.00 ± 0%  -75.00%  (p=0.000 n=20+20)
RGB_full-8      4.00 ± 0%      1.00 ± 0%  -75.00%  (p=0.000 n=20+20)
```