getUsers and repository sizes

Includes changes from #74 and #73

• add getusers in group, and LastAuthenticationTimestamp in user
• get repository sizes

target .Net Standard 2.0

refactor project to only target .Net Standard 2.0

0.1.2 Alpha release

Features:

• manage Stash 'Projects' (get information, create and delete capabilities)
• manage Stash 'Repositories' (get information, create and delete capabilities)
• manage Stash 'Branches' (get information, create and delete capabilities)
• get information about 'repository files'
• get information about 'Commits' and 'commit changes'
• get information about 'Tags'

Norm MacLennan contribution:

• get branches by commit id
• get file contents

0.1.1 Alpha release

Features:

• manage Stash 'Projects' (get information, create and delete capabilities)
• manage Stash 'Repositories' (get information, create and delete capabilities)
• manage Stash 'Branches' (get information, create and delete capabilities)
• get information about 'repository files'
• get information about 'Commits' and 'commit changes'
• get information about 'Tags'

New features:

• adding CREATE and DELETE capabilities to 'branches'

0.1.0 Alpha release

Warning this package isn't backwards compatible

Functionality changes:

• More comprehensive API abstraction.
• API actions organized by Stash area (like projects, repositories, branches, etc)

New features:

• refactored StashClient class. Use it to access APIs actions (StashClient.Projects.{Action})
• Added GET capabilities for 'branches' and 'commits'
• Added DELETE capabilities for 'projects' and 'repositories'