TTF cache support

[bluewaysw]

Building a cache that keeps already computed table for the fonts to be reused later. This will speed up the operation, especially on low end systems.

[bluewaysw]

To make the cache approach more efficient Iadjusted the threshold for using available kerning information.

The current implementation uses KERN_VALUE_DIVIDENT 100 which translated to "starting at 1% character width of kerning information it is consided for geos rendering".

The following experiments lead to "DIVIDENT -> kern entry count used" for the "Nimbus Sans" font.

100 -> 0x567
40 -> 0x2a5
36 -> 0x278
34 -> 0x261
30 -> 0x1e7

I decided to go with 30, pre-installed cache has been computing using this threshold.

[bluewaysw]

The preinstalled cache is build (using an GeoWrite document containing all relevant glyphs) for all pre-installed font and styles with the following sizes: 10, 12, 14, 18 (as those are the sizes that are delived as bitmap variants for the original nimbus FNT font files)