Fixed #185

* added VisibilityLevel, LSF and Request Access to Group creation API

* Updated Groups API to support group update and LFS/RequestAccess enablement

* Added Version API support

* #172 Version API: fixes as per maintainer's requests

If a project is a fork it will show the details of the project that
it was forked from.

If a project isn't a fork the setting will be null.

The V3 API is deprecated and the static V3 docs are no longer hosted at the primary docs location.

This change breaks backwards compatibility.

The BranchesService methods were almost all inconsistent with other Services and not supplying all available options. Also updated all documentation links.

The Branch struct now includes all properties exported by the v3 API.
ListBranches takes a new ListBranchesOptions struct for pagination.
Added the ability to configure the branch protection in line with API documentation.
Added a new DeleteMergedBranches which is part of the branches page.

* Add Build Trigger endpoints

* Update variable name

* Add a WithContext function, Fixes #143

This enables the use of requests with a specific context attached.

* Fix indentation

* Add a test

Fixes #145.

This adds the `can_push` option to the AddDeployKeyOption and DeployKey structs, in line with what is supported by GitLab.

* Add statistics information and flag to query options

* groups do not expose a CommitCount

* make the sizes unsigned, negative values dont make sense

* repair tests

* add review comments

* remove wrong tagging from field

* Adds support for creating commits

* Adds support for cherry-pick commits.

* Fixed indentation

Add missing fields

This also renames the Go field, which may break things. Probably not a
lot though - ParentIds never had any content.

This typo probably is a result from invalid Gitlab API documentation
on tags, which also wrongly uses `parents_ids`.

I created a merge request there as well:

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9550

It looks like these options functions are pretty much always called `With…` which makes them better recognizable. So I renamed the `SudoUser` func as well as the `SudoFunc` type to make them more generic and idiomatic.

https://docs.gitlab.com/ce/api/README.html#sudo

Updated:
- GetMergeRequest
- GetMergeRequestChanges
- UpdateMergeRequest
- AcceptMergeRequest

* Correctly parse/unmarshal validation errors returned from the API

* Refactor/fix error handling