Initial work on WebVTTParser class
Implemented collectDigits, collectWord, and skipWhitespace

Also moved isAsciiDigit and isHtml5Space to new Char class,
so that they are in a more central location.
Implemented WebVTTParser::parseHeader() V1, with synchronous tests

It will be simpler to make the parsers work with SynchronousBuffer
first, so for now all tests for the parsers involve SynchronousBuffer
Slightly more robust synchronous WebVTT parseHeader tests
Re-organized header parser for re-entrant calling

Also enables testing individual sections of parseHeader(),
which is nice.
Implemented WebVTT document parser, and additional string helpers

String helpers include parseInt(), which parses an integer from a
given position with a radix of 10 (Perhaps a future version may be
added later which is more flexible).

Additionally, another one will skip HTML5 space characters, and
there is additionally a new substring method, however it is likely
to be broken due to refcounting issues, and will need some testing.

Unit tests for these new methods, including the document parsing,
are forthcoming.

Note that the document parser is still not able to actually dispatch
Cues to the client, as cues have not been properly defined as of yet.
Further, there is still no support for dispatching errors to serve
linters/validators. Sorry!
Added unit tests for new String methods

New unit tests for String::parseInt, String::skipWhitespace, and
String::substring. Cheers.
Fix Buffer.getline() +added CollectTimingsAndSettings tests