* add EMail endpoints from gitlab api

* added changes requested

- gitlab.CreateProjectOptions.ContainerRegistryEnabled
- gitlab.Project.OnlyAllowMergeIfBuildSucceeds
- gitlab.Project.LFSEnabled
- gitlab.Project.RequestAccessEnabled
- gitlab.Project.ContainerRegistryEnabled

* add parameters “since” and “until”

* update API Docs URL

* closes #77 - adds `web_url` field to `Issue`

* Add new fields in Issue struct to bring it up-to-date with Gitlab API

The following fields have been added to `Issue` struct
* `Subscribed`
* `UserNotesCount`
* `Confidential`
* `DueDate`
* `WebURL`

Add ops is equal to null judgment

https://gitlab.com/gitlab-org/gitlab-ce/issues/21468

Tags is now a separate service, following the Gitlab API structure.

* Add support for /projects/*/builds/*
PR for issue #42

* fix

* modify comments

* modify comments

* change styles and perform some addtion/deletion according to comments

* define Runner as a independent type

* define ArtifactsFile as a independent type

* remove type Runner and ArtifactsFile, and remove field Coverage

Check out http://docs.gitlab.com/ce/api/users.html

added web-hooks: tag_push_events, note_events, build_events, pipeline_events, wiki_page_events, enable_ssl_verification (#69)

* Simplify some code via gosimple

See https://github.com/dominikh/go-simple.

* strings: use bytes.Buffer directly

It has methods to write strings and bytes already, which is much easier
and also faster than going through a regular write of []byte.

* Run go fmt

* CI: Bump Go versions

Convert all *Options structs to use pointer for fields and fixup the README and project struct (#66)

* Convert all *Options structs to use pointer for fields, per #29.

* Update README and fix project struct

The `project` struct was the only one that had all pointers, so I reverted that to make things consistent again.

The same goes for the `time.Time` pointers. In some cases the API does not return a time and if the field is not a pointer to `time.Time`, this will generate an error. So to be consistent now all `time.Time` fields are pointer fields.

support oauth token.

additional fields in Gitlab

Add archive/unarchive support

Support the last_sign_in_at user field

labels: marshal error fix

Fix label marshalling

Fixes an internal server error when no label available

Error occurs when trying to create an issue with no labels at all. In
this case, the POST body parameter will be `"labels":[""]` instead of
the expected `"labels":[]"`.

Add DeleteIssue() method