[psCharStrings] Shorten output of encodeFloat

[dscorbett]

This optimizes fontTools.misc.psCharStrings.encodeFloat to return shorter outputs. There are three independent optimizations:

• Use exponential notation for multiples of 1000. For example, 10000 was encoded as 1e 10 00 0f but is now 1e 1b 4f.
• Never use a decimal point and an exponent in the same number. For example, 12345678000 was encoded as 1e 1a 23 45 67 8b 10 ff but is now 1e 12 34 56 78 b3 ff.
  • Furthermore, don’t use an exponent at all if this optimization would otherwise produce an exponent of 1. For example, 909876540 was encoded as 1e 9a 09 87 65 4b 08 ff but is now 1e 90 98 76 54 0f.
• Remove leading zeros from exponents. For example, 100000000 was encoded as 1e 1b 08 ff but is now 1e 1b 8f.

Sometimes the new output is not shorter (e.g. 1e e1 00 0f vs. 1e e1 b3 ff) but it is never longer.

[behdad]

Thanks. Can you do the same in HarfBuzz's encode_num_tp function?