Add wikis api

Signed-off-by: Stany MARCEL <stanypub@gmail.com>

Tweak PR #222

Fixup PR #222 just a little. Most important fix that was needed, was the return type used for the Get call.

Adding GET request for Slack Integration on a Project

Implements all methods of the Wikis API Introduced in GitLab 10.0.

https://docs.gitlab.com/ce/api/wikis.htmlSigned-off-by: Stany MARCEL <stanypub@gmail.com>

Reorder the fields so they match the docs and add `parent_id`

Fixes #217

Fix typo in MR options

Fix typo `omitemtpy` to `omitempty`

Refactor PR #204

The API call for getting MR Approvals was missing from the current
package, so added in the correct struct and request to get a single
MR's approvals.

Fixes #205

* Fix the PipelineEvent struct, with proper sub struct for Runner and correct type for the artifacts_file 'size' field

* Updated tests for changes to PipelineEvent

* Formatting

* Naming

* BuildEvent BuildDuration is a float, not a string

* float64

* Fix the PipelineEvent struct, with proper sub struct for Runner and correct type for the artifacts_file 'size' field

* Updated tests for changes to PipelineEvent

* Formatting

* Naming

So no content is given, which is in contrast with the API docs and makes this a backwards incompatible change.

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