fix random log output

the char array returned by git_oid_fmt isn't null terminated and then
passed to a format specifier with %s. Output is thus the SHA + gargabe until a \0 is found.
Fix it by increasing the array by 1 and using git_oid_tostr which adds a \0.
Merge pull request #235 from diederich/fix/errorOutput

fix random log output
Add CONTRIBUTING.md

The lack of this could explain the wild variation in styles we have seen from our recent contributions.
++specta and expecta
Add writeTree method to GTIndex
Add spec for GTIndex writeTree method
fix that could not update the submodule
fix build path error
Merge pull request #236 from isaac/index-write-tree

Add writeTree method to GTIndex
Update to upstream libgit2
Revert "fix build path error"

This reverts commit 40e915aee1d952c005c4025108121e6be99d9183.
Merge pull request #237 from welsonla/master

fix that could not update the submodule
Tiny typo
Merge pull request #242 from Uncommon/typos

Tiny typo
Add OpenSSL-iOS target that builds OpenSSL for iOS
Use the correct argument for the format string
Allow nil descriptions and failure reasons
Test NSError+Git formatted strings
Merge pull request #243 from libgit2/fix-error-format-string

Use the correct argument as the format string
Add the no-gost option to openssl build configuration