[feaLib] add support for Character Variants FeatureParams

[anthrotype]

feaLib currently supports featureNames tags to add FeatureParams tables to stylistic sets (ssXX) features.

To support Feature Parameters in Character Variants features (cvXX) feaLib should add support for "cvParameters":
http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html#8.d

Also see the definition from OT spec under Tag: 'cv01' - 'cv99':
https://www.microsoft.com/typography/otspec/features_ae.htm

And in otData.py:

fonttools/Lib/fontTools/ttLib/tables/otData.py

Lines 72 to 81 in 0cc1721

	('FeatureParamsCharacterVariants', [
	('uint16', 'Format', None, None, 'Set to 0.'),
	('NameID', 'FeatUILabelNameID', None, None, 'Feature UI label NameID.'),
	('NameID', 'FeatUITooltipTextNameID', None, None, 'Feature UI tooltip text NameID.'),
	('NameID', 'SampleTextNameID', None, None, 'Sample text NameID.'),
	('uint16', 'NumNamedParameters', None, None, 'Number of named parameters.'),
	('NameID', 'FirstParamUILabelNameID', None, None, 'First NameID of UI feature parameters.'),
	('uint16', 'CharCount', None, None, 'Count of characters this feature provides glyph variants for.'),
	('uint24', 'Character', 'CharCount', 0, 'Unicode characters for which this feature provides glyph variants.'),
	]),

[anthrotype]

Fixed by #1169