matplotlib Code

added a few incomplete backend APIs

reorganized backend_api so we can include numerous backends in seperate
html pages

updated configuration api

use htmlonly directive to cleanup a few items in the pdf document:
link to pdf download
release, date and comment at beginning of each part which was poorly
formatted and somewhat redundant in the pdf document

minor formatting changes in documentation

added api file for matplotlib configuration

added customization api, fixed a few errors in docs

added backend bases api

fixed a doc error in patches

applied gregors agg resample patch