Add summary for the Hangfire NuGet package

Bump version to 1.5.6

Add release notes for 1.5.5

Temporary skip symbols (nuget.smbsrc.net is down)

Update release notes for 1.5.4

Bump version to 1.5.3

Bump version to 1.5.2

Add release notes for 1.5.1

Merge pull request HangfireIO#454 from HangfireIO/dev

Release 1.5.0

Disable flapping test

1.5.0 release contains another implementation of this logic.