SIP v6.6.0 Snapshots

[Phil Thompson]

The next SIP snapshot will be of v6.6.0. This implements the first stage 
of making SIP a pure Python implementation by replacing the .sip file 
lexer and parser (originally flex and bison) with ones implemented using 
PLY. There are a small number of user-visible differences...

- it is slower (for now)
- error messages (from the parser) are much improved
- parsing will continue after errors (the old parser stopped at the 
first error).

The generated code is identical byte-for-byte to previous versions. If 
not then please report it as a bug. SIP v6.5.5 introduced the 
--no-compile and --no-version-info command line options to sip-build. 
The purpose of these is to make it easier to compare the code generated 
by v6.5.5 and v6.6.0 to ensure they are identical.

Phil