TTF:Vhea - Vertical Header table
This is a simple table with just standards specified instance variables
| 
    version
    Ascender
    Descender
    LineGap
    advanceHeightMax
    minTopSideBearing
    minBottomSideBearing
    yMaxExtent
    caretSlopeRise
    caretSlopeRun
    metricDataFormat
    numberOfVMetrics
 | 
Reads the table into memory as instance variables
Writes the table to a file either from memory or by copying.
Updates various parameters in the hhea table from the hmtx table, assuming
the hmtx table is dirty.
None known
Martin Hosken Martin_Hosken@sil.org. See PDF::API2::TTF::Font for copyright and licensing.