Added src/Makevars to .gitignore
Updated Makevars.win
Merge branch 'master' of https://github.com/stewid/git2r

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Added slot path to git_repository

Ongoing work to remove the usage of external pointers and instead only
keep the path to the repository.

* Replaced the the external pointer repo to a git repository with the
  path to a git repository.

* Removed the the external pointer to a git_revwalk.
Updated .gitignore
Updated git2r.c

* Changed code to work with the path to a git repository and not an
  external pointer to a git_repository.
Fix init of a new Git repository
Updated documentation
Bumbed version to 0.0.6
Updated Makevars.win
Added method to add files to repository index
Updated NAMESPACE with export of method add
Updated documentation with methods add
Added git_signature show method
Added method default_signature

Get the signature according to the repository's configuration
Updated documentation
Added error message for invalid repository
Fixed error checking when adding a file
Open S4 repository return NULL instead of error on failure

When opening the repository from the S4 class git_repository repo
slot, the function now returns NULL instead of throwing an error.
Fixed error checking when listing references