Tdewolff-minify

- HTML: ignore CSS minification for `amp-boilerplate`
- HTML: add `KeepQuotes` option for attributes
- XML: bugfix for recent changes to XML parser

Upgrade to tdewolff/parse2.3.14:
- Re-parse input immediately when encountering parse error. Previously this was only done if the error was actually read which would save us from re-parsing the file (i.e. better performance). However, an error is (a) rare and (b) happens only once per file. Re-parsing on errors does not impact the performance of well formatted files, and a reliable error message is valued more.
- Bugfix: prevent infinite loop on error on input file that contains unicode code points (i.e. any character bigger than `0xC0` usually followed by more bytes).
- Improve error messages for parsers to include parser name and print offending byte(s)

* CSS: remove space after function in property value; `margin:calc(10px) calc(20px)` => `margin:calc(10px)calc(20px)`
* SVG: parse `A` path command correctly when the booleans `largeArc` and `sweep` are not separated by a space, such as in `A10 10 0 0120 0` which is equivalent to `A10 10 0 0 1 20 0`
* SVG bugfix: make sure we are processing a valid path command
* SVG bugfix: prevent panic when having insufficient path arguments
* cmd: surpress error when minifying empty directory
* HTML: only minify attributes for known HTML5 tags, fixes 270
* HTML, XML, SVG: minify entities with parse2.3.13 such as: `" => "`, `&34; => "`, `&x22; => "`, `’ => ’`, `&x270F; => &9999;`.

Bugfixes:
- SVG: don't convert polyline/rect/polygon/line to path, which can break CSS, fixes 260
- SVG: relative SVG Bézier commands not properly minified
- CSS: don't remove whitespace in nested unknown at-rules, fixes 262
- CSS: fix panic for `background` when it contains functions other than `calc` for `background-position`, fixes 263
- CSS: fix panic for `background-position` with three numbers
- CSS: fix panic for url() with only whitespace or only one quote

* Remove import comments
* SVG: do not convert line/rect to path if coordinates are relative percentages
* CSS: fix bug with inline CSS encountering `}`

* CSS: fix position information in error context
* CSS: fix `background-position` panic with offsets that are zero
* HTML: trim and collapse whitespace in certain attribute values
* SVG: shorten cubic and quadratic Beziér path data to their shorter format or to line segments