Added useful optional arguments to bItalic().

The parameters are:
    1. Italic angle (as implemented previously).
    2. Italic xheight, as a fraction of the font xheight.
    3. Flags: an integer composed of the following bit values:
       * 0x0001 = Transform bottom serifs.
       * 0x0002 = Transform serifs at x-height.
       * 0x0004 = Transform serifs on ascenders.
       * 0x0008 = Transform diagonal serifs.
       * 0x0010 = Create italic a from the bottom half of italic d.
       * 0x0020 = Give italic f a long tail.
       * 0x0040 = Give italic f a hook.
       * 0x0080 = Remove serifs from descenders.
       * 0x0100 = Special handling for Cyrillic phi.
       * 0x0200 = Special handling for Cyrillic i.
       * 0x0400 = Special handling for Cyrillic pi.
       * 0x0800 = Special handling for Cyrillic te.
       * 0x1000 = Special handling for Cyrillic sha.
       * 0x2000 = Special handling for Cyrillic dje.
       * 0x4000 = Special handling for Cyrillic dzhe.
    4. Serif type: 1=flat, 2=simple slant, 3=complex slant.
    5. LSB change: left bearings will be multiplied by this factor.
    6. Stem width change: stem widths are multiplied by this factor.
    7. Counters change: counters will be multiplied by this factor.
    8. Stem width change for lowercase characters; defaults to #6.
    9. Counters change for lowercase characters; defaults to #7.
Documented the Italic() native scripting function.
Added scripting functions SelectGlyphsSplines, SelectGlyphsReferences

Added scripting functions SelectGlyphsSplines() and
SelectGlyphsReferences(), respectively for selecting glyphs with only
splines and only references.  (SelectGlyphsBoth was already present.)
These functions work similarly to the menu commands in the UI; they
take no arguments.
Added ChangeWeight native scripting function.

Added ChangeWeight() function for boldening and unboldening.  It takes
one argument which is the weight change in em units.  Positive values
make the selected glyphs bolder; negative values make them less bold.
Added "Class" parameter to GlyphInfo native scripting function.

GlyphInfo() may now be passed the string "Class" as its first
argument, and it will then return a string corresponding to the glyph
class of the selection, which will be one of "automatic", "none",
base", "ligature", "mark", "component", or "unknown".
Documented SelectGlyphsReferences and SelectGlyphsSplines.

Also added index entry for SelectGlyphsBoth which was missing.
Documented the ChangeWeight() native scripting function
Documented the Class parameter to GlyphInfo()
Merge pull request #1055 from blipvert/fixes/21

New scripting functions: SelectGlyphsSplines, SelectGlyphsReferences, ChangeWeight, and "Class" tag to GlyphInfo()
Merge pull request #1054 from blipvert/fixes/20

Added useful optional arguments to the Italic() native scripting function