Allow None for globalSubrs in T2CharString
Handle and warn about out-of-order Coverage table entries

Apparently the SIL Gentium fonts have wrong sorting in Coverage
tables.  That's broken by the spec, but shapers still work with
such fonts.  So, we warn when reading, and when writing, such
out-of-order coverage tables.
Fix parsing of hinting instructions that end in a PUSHB

Sounds useless, but MReifutaiM-Regular.ttf seems to have that, and the
parsing back from XML was failing because we expected a token whereas
after dropping whitespace there wasn't any left.
[subset] Protect against missing rulesets

Fixes subsetting Molengo-Regular.ttf.
[subset] Fix against missing AttachList entries
Make BaseTable a new-style object
Load all OpenType sub-structures lazily

Huge win for subsetter and anyone else who doesn't need the entire
tables.  Subsetting a huge font (eg. NotoSans-Regular.ttf) to a
small set (say, main Cyrillic characters) is something like six
times faster now.  Bulk of time was being spent in blowing up the
GPOS kerning pairs and attach points.  Now we don't load those if
they won't be in the final subset.

Slight slowdown for usecases that need the entire table.
Minor
Merge branch 'master' of https://github.com/moyogo/fonttools
Merge remote-tracking branch 'upstream/master'