Updates to the AviSynth C API wrapper
Add option for parsing on start the autoloaded avsi files for script functions

Some changes to the parsing:
- Not add parsed defaults values for doubtful cases.
- The name of the argument was missing for arguments that don't accept being
  called by name.  Still it's an useful info as it's shown on the autocomplete
  tooltip.
Small change to AviSynth internal functions classification
Add syntax for function parameters not included by default in autocomplete

Example (Blur):
  (
  clip,
  float amount=0.00 (0.00 to 1.58),
  [float amountV=0.00 (0.00 to 1.58)],
  bool "MMX"=True
  )

amountV won't appear on the autogenerated autocomplete preset.  Some
useful cases:

- New parameters added in AviSynth 2.6 to the internal filters
- Optional parameters without a default value, like filepaths
- Functions with a huge number of parameters, some of them rarely used

This can't be combined with the [, ...] notation for multiple clips/paths
unless written as [...]
Some fixes to the parsing of the filter database