Update defs for libgit2 0.18

These are automatically generated definitions, with many
inaccuracies.
Add myself to travis notification list
Improve function signature parsing
Use pkg-config to find out location of headers
Refactor the building of git2.nci and fix a bug in 'make clean'
De-duplicate conf folder
Change default fallback to PMC.
Merge branch 'nciupdate'