Allow parse/write without escaping.
Allow parse/write without escaping.

Unescaping, among other things, strips quotes, and Glyphs files
somewhat arbitrarily quote numbers.  This means we cannot round trip
parsing of Glyphs files, which introduces noise in the diffs when trying
to read/patch/write files from tools.  Allowing suppression of
unescape/escape makes it possible to limit the changes to only those
that are intended.

Tools modifying the parsed data must make sure any modifications are
properly escaped before writing new data.  The unescaping/escaping
code was moved into static methods on the Parser/Writer classes to
facilitate this.

googlefonts/glyphsLib,googlei18n/glyphsLib