v4.2 with server auto-start functionality and other features and bugfixes

• omnisharp-emacs now attempts to auto-start the server when opening C# files, #287
• adds the omnisharp-solution-errors command to list all errors/warnings on all files in the solution loaded
• on macOS and Linux omnisharp-emacs now downloads OS-specific version of omnisharp-roslyn server. this drops dependency on mono.
• a couple more of performance and bug fixes, listed https://github.com/OmniSharp/omnisharp-emacs/milestone/2?closed=1

v4.1 with several months' worth of fixes after the first roslyn release

This releases fixes several of the bugs encountered since 4.0 version which transitioned to omnisharp-roslyn server, including automatic server installation, metadata browsing and more.

v4.0 release with support for omnisharp-roslyn

Merge pull request #312 from supermomonga/auto-complete-show-kind-fea…