Small improvements to 'use file'

Add separate function to get list of generated files, which may be
useful to users that don't wish to go 'all the way' and use
sbk_wrap_library. Always de-duplicate includes and typesystems up front
so that we don't have duplicates in properties (also allows us to get
rid of sbk_cat_no_dups). Keep global header and typesystem together in
arguments when invoking shiboken, rather than separated by other
options.

Change-Id: I2bd16c41f5d11f92c075133bba67731ade01c32c
Document 'use file'

Add reStructuredText documentation to UseShiboken.cmake. This is done in
the upcoming CMake 3.0 style using lua-style bracketed comments, which
is convenient for editing as it is more likely that editors will be able
to apply syntax highlighting for this style. In order to maintain
compatibility with CMake 2.x, a small Python script converts these to
regular, single-line comments before the file is installed.

Change-Id: Ia4a963e5363bf865d31fad7cfe123a491efd5b8f