tests: new fancy asserts are for Python 2.7 only
ci: add all Python versions listed as supported in README.rst
Merge remote branch 'cboos/fix-test-asserts-for-python26'
Create Config type
Add getter for global and system config
Implement addition of files to Config
Add back reference from Repository to Config
Implement dictionary-like behaviour for Config
Wrap git_config_foreach in Config
Implement getting and setting of multivars
windows: detailed build instructions

The default build of libgit2 with `__stdcall` calling
convention is inadequate. We need to use a more standard
`__cdecl` build, which can be obtained by specifying
`-DSTDCALL=OFF` while configuring libgit2.

Also mention the LIBGIT2 environment variable (2b4e5504).
Merge remote branch 'cboos/windows-build-instructions'
documented `create_commit` in README
Fixed bug in test_add.
Initialize variables in Config_set_multivar with NULL
Fix unit tests for Python 2.6
style: remove trailing white-spaces
tests: don't leave test files behind
Fix errors detected by pyflakes
Add .mailmap file