Tdewolff-minify

- CSS: fix minification of `flex`, default of `flex-basis` is zero for three value case, fixes 292
- CSS: remove whitespace within `import url(...)`, fixes 296
- HTML: remove spaces around/in picture and audio following whitespace removal rules for phrasing elements

- external minifiers can now use input/output files instead of only stdin/stdout using the `$in` and `$out` keywords
- SVG: don't minify inside `foreignObject`, fixes 291

- SVG: bugfix for `C`, `S`, `Q`, and `T` commands where if the control points would not overlap with the start or end points of the curve, it would still be converted to a line.

- DataURI: if the original data URI is shorter than the URL-encoded/base64-encoded URI, use the original instead, fixes 282
- Bugfix: decimal (i.e. without exponentials) incorrectly minified 139.9 to 230 instead of 140

- Use custom URL encode/decode functions to fix 180 and 243
- `Decimal` and `Number` now take precision to mean the number of significant digits, and not the number of digits behind the dot (decimals); includes a few subtle bugfixes. `Decimals` option renamed to `Precision`
- Move `Hash` definitions and `EntitiesMap` from `tdewolff/parse` to this repository to prevent releasing new versions of `tdewolff/parse` everytime
- cmd: add `--sync` functionality
- cmd: make `--watch` work for newly created directories
- cmd: various fixes and improved messages
- CSS: keep quotes around IE font families, fixes 251
- CSS: major refactor to allow nested functions to be minified
- CSS: improved HSL/RGB minification
- CSS: minify more properties: `color`, `background-color`, `border-color`, `border-*-color`, `caret-color`, `outline-color`, `fill`, `stroke`, `column-rule`, `text-shadow`, `text-decoration`, `text-emphasis`, `flex`, `flex-*`, `order`, fixes 217
- CSS: minify `background` better if it has multiple layers
- CSS: improve `box-shadow` minification
- CSS: accept CSS functions where numbers/lengths are required, such as `calc`, `min`, `max`, `clamp`, `attr`, `var`
- SVG: print new path command after bad command, fixes 275
- SVG: print `A` command correctly with boolean `largeArc` and `sweep`
- SVG: avoid precision errors for alternative (absolute or relative commands) path

Add `install.sh` and `Makefile` to `./cmd/minify`.

No changes to binaries (use v2.6.2).