Tdewolff-minify

- Incorporate the `parse` dependency into this repository
- cmd: fix forward/backward slash for Windows platform, fixes 403
- JS: add space to `a<!--b` and `a</script>/` in more instances to avoid confusion with operators, see 413
- JS: add variable scope to switch statement
- JS: parse `async(a)` as possible expression or arrow func, fixes 406
- JS: fix lexical variable renaming for descoped, fixes 405
- JS: fix import statement/call parsing at module level, fixes 399
- JSON: add `KeepNumbers` option, fixes 400

- keep minimal Go version at 1.13 (and not 1.16 which is more convenient for cmd)
- cmd: fix regression for stdin/stdout, fixes 392
- HTML: update error line and column for errors from other minifiers
- CSS: KeepCSS2 (for IE11) doesn't use initial for background-color, fixes 394
- CSS: keep integers for z-index even in functions such as calc, fixes 395
- CSS: fix minify to initial/auto/none for flex, fixes 398

- JS: accept shebang comment as first line, fixes 345
- HTML: update fix for space after `<i></i>`, see 390
- CSS: unicode-range minification, fixes 321 and closes 344

- cmd: create missing directories for symlinks, see 385
- cmd: preserve file permissions, see 385
- cmd: wait 0.1 seconds before processing watched file change, fixes 372
- cmd: watch now works with file input and output (not just dirs), see 372
- cmd: fix watch functionality for unknown file extension even if --type set, fix watch when src is not a dir; see 372
- cmd: follow symlinks by default, new -p options will copy symlinks without following them, fixes 385
- cmd: use io/fs and demand Go1.16, see 388
- JS: add &&= ||= ??= operators, see 380
- JS: add support for class field definitions, fixes 380
- JS: fix recursion limit in string merging, fixes 382
- CSS: don't remove dimension for zero values inside functions like var and calc, fixes 371
- SVG: don't minify extremely long path data (OSS-Fuzz)
- HTML: keep space after empty `<i></i>`, fixes 390

- JS: fix bugs related to the 'use strict' directive prologues at the beginning of functions and modules, fixes 376
- JS: export statement's function name must remain for non-default declarations, fixes 375
- CSS: prevent quasi-infinite recursion in background's append, from OSSFuzz

- JS: write final ) in ()=>({}), fixes 369
- JS: keep debugger statements, fixes 370
- JS: support ellipsis operator anywhere in arguments, fixes 373
- JS: limit recursion in string merges, from OSSFuzz