Update the go-gitlab package to support the V4 API

* add search query into merge requests and issues

* Moved TimeStats to Issues, added time_stats functions to merge_request

Kept time_stats.go for backward compatibility

* add fields to struct UpdateMergeRequestOptions

* Refactor PR #193 a bit

* Delete deprecated `upvote` and `downvote` fields

* Add http status `Accepted` (202) as successful status

* Rename the milestones field `iid` to `iids` (`[]int`)

* Update the copyright lines

* Add the project members calls to a new service

* Moved PUT to POST for /users/:id/(block|unblock)

* Renames `branch_name` to `branch` where applicable

* Add Feature Flags baseline

This commit adds the service, ensures that the service gets instanciated
with the rest and provides the required types and method to list
features flags.

* Add SetFeatureFlag method to FeaturesService

This commit allows to create and modify feature flags by setting their
values

* Change doc urls and simplify use of values according to docs too

Fixes #185

* Supports v4 get repository files

* update exmaple of repository files

* Add Impersonation Tokens Support and Add missing field to CreateGroupOptions

* Fix ImpersonationToken Example

* Add comment again that was mistakenly deleted

* Fix CreateImpersonationTokenOptions

Fix CreateImpersonationTokenOptions for ExpiresAt can be empty

* Update impersonation.go

* Remove not existent option field

* Fix pointers and insert 'omitempty'

* Update documentation links

* Adjust review considerations

The groups.go file still needs to be split into a groups.go and members.go file. But I’ll leave that for a later PR.

* Added Version API support

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

* Fixed GitLab APIv4 support
Signed-off-by: Mikhail Grigorev <sleuthhound@gmail.com>

* Fixed test for APIv4
Signed-off-by: Mikhail Grigorev <sleuthhound@gmail.com>

* Fixed Statistics options
Signed-off-by: Mikhail Grigorev <sleuthhound@gmail.com>

* Add group share options to projects

* Fix group visibility level

* changed comment

* Fixes: visibility level and share group options
Relates to PR #167

* Fix: tests adapted

* Fix: changed all 'visibility_level' to 'visibility'

* Changed VisibilityLevel pointer

* Adding Todos API resource

* Adding TodoTarget struct to support Todo types (#165)

 Author:    Erick Guevara <erick.guevara@gmail.com>

* Return basic info about pipeline in GET /projects/:id/pipelines

* Adds pipeline example

* Rename RootPipeline to PipelineList with type []struct

* Change `IID` to `IIDs` where applicable

* Remove the `/project/search` endpoint

Instead `/project?search=query` should be used to search a project. This endpoint already exists as the `ListProjects` function already contains a `search` option.

* Do not return deprecated field `expired_at`

* Change `keys` to `deploy_keys`

And add all missing `deploy_keys` endpoints.

* CI: always test on the latest bugfix Go releases (#154)

* Remove unnecessary fmt.Sprintf call (#153)

* Fix typo in user 404 error (#155)

* Update BranchesService Methods.

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.

* Restore API doc links

* Add StatusNoContent as successful status.

See documentation for expected return statuses: https://docs.gitlab.com/ce/api/README.html#status-codes

Also change the codes to http library codes.

* Change Build Triggers to PipelinTriggers.

This is in line with the updated v4 API. See https://docs.gitlab.com/ce/api/pipeline_triggers.html and https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9713 for more information.

* Move Pipeline Triggers to a separate file.

Creates the new service PipelineTriggersService for handling requests to the Pipeline Triggers part of the GitLab API.

Fixed #185