- write documentation for CWB::CL package

Version 3.0

This is the first official release of the redesigned Perl API for the low-level CL library.
It is compatible with version 3.0 of the IMS Open Corpus Workbench.

New features:

  - all "scalar" CL functions are now vectorised in the XS/C code, making them up to
    4x faster if called with long argument lists

  - Perl wrappers around the API functions have been eliminated wherever possible