Additionally updating existing *Options to include:
 - UpdatedAfter/Before - "Return merge requests updated on/before/after the given time"
 - SourceBranch- "Return merge requests with the given source branch"
 - TargetBranch - "Return merge requests with the given target branch"
 - Search - "Search merge requests against their title and description"

Corrected some outdated documentation.

More info here: https://docs.gitlab.com/ce/api/merge_requests.html#list-group-merge-requests

* projects.go: adding approvals_before_merge to CreateProjectOptions

* project.go: updating gitlab api doc ref to reflect change to CreateProjectOptions

* Implement DownloadSingleArtifactsFile

* Fix bad variable name

* Fix function docstring

* Make jobID an int var

* Use QueryEscape for consistency

* Dont escape filepath

* Fix typo

* Add weight field to UpdateIssueOptions struct

* Fix weight field order

* Update runners: add maximum_timeout option

* Update runners: add new methods and tests

* Update runners: fix typo on token

* Supplement Slack service

Refs:
- https://docs.gitlab.com/ce/api/services.html#slack-notifications
- #142

* gitlab: move BoolValue type and associated methods to gitlab.go

* services: update slack service: add url tags, fix typo, remove pointers in properties

* Revert renaming webhook field

* Fix ListProjectContributionEvents fails with 404 error (#449)

* Rename EventsService.ListProjectContributionEvents to EventsService.ListProjectVisibleEvents to match with gitlab API changes

* Adding missing straight option in repositories compare api

* Fixing struct reference for missing straight option

Adding support for 'list-merge-requests-associated-with-a-commit' (reference: https://docs.gitlab.com/ce/api/commits.html\#list-merge-requests-associated-with-a-commit) (#447)

* Adding Group Variables support

* Fixing naming per request

* Fixing merge conflict

* Fixing merge conflict

* Adding support for group issue boards

* Cleaning up comments and renaming GetGroupIssueBoardLists() to ListGroupIssueBoardLists() to match the gitlab API spec.

* Fixing comment lengths

* Adding Project Variable Support

* Adding missing semi-colons

* listtagopts added params

* test fix + gitignore

* added commit missed functionality

* rename vars

* docs fix

* requested changes

* type mistype

Ref: https://docs.gitlab.com/ce/api/issues.html#edit-issue

Ref: https://docs.gitlab.com/ce/api/award_emoji.html#award-a-new-emoji

* add pipeline to merge request

* sha in caps

ci skip

* Fixes https://github.com/xanzy/go-gitlab/issues/407
* Add the first groups unit test

* Allow users to pass the base URL without the API info

* Makes SetBaseURL more robust by matching on apiVersionPath suffix and adds unit test (#405)

* Fix tests