Support of Discussion API for issues and merge requests

(fix tests)

Merge pull request GitLabPHP#331 from woodylan/master

support impersonation tokens

iid instead of id in issue contruct

Bumped branch alias

Merge pull request GitLabPHP#297 from m-bymike/master

fix issues with symfony options resolver

Merge pull request GitLabPHP#276 from b0nd0/master

Branches containing a slash break v4 branch endpoints. GitLabPHP#263

Merge pull request GitLabPHP#269 from dylangl/master

add params id fork

Merge pull request GitLabPHP#266 from Seretos/master

fix link for pipeline creation

Merge pull request GitLabPHP#251 from c33s/feature/variables-enhancement

Updated addVariable() and updateVariable()

Merge pull request GitLabPHP#244 from KyleWiering/Issue-242

GitLabPHP#242 Gitlab/Model/MergeRequest methods fails on incorrect id usage