cache - allow access to old (outdated) entry when creating cache entry

this allows to reuse the SourceText object which will enable incremental
parsing/updating of syntax trees
buffersync - introduce a SourceTextService to allow buffer updates

Makes the Rolsyn compiler ask for source text from a service when building
syntax trees. Allows to record source text changes when a corresponding
messages is being received
buffersync - incorporate feedback
buffersync - incorporate feedback
buffersync - incorporate feedback
buffersync - sorted usings
Make preprocessors actually work on CoreCLR
- Introduced IAssemblyNeutralInterfaceCache interface since we need
these to be loaded once per app domain. All child load contexts
need to use ANIs that have already been loaded earlier.
- Enhance fallback loader logic so that it takes host loaded assemblies
into account for child loaders.

#829
Removed unused accessor
Updated to the new TFM
Add default Win32 resource when emit assembly

This change will enable the proper information be showed in file property
through Windows Explorer
Add all sub directories as a cache dependency
- In VS adding an empty folder then adding a file
doesn't bust the cache.
Merge branch 'release' into dev
Added package descriptions
Merge branch 'release' into dev
Merge pull request #767 from jrieken/buffersync

dth - enable buffer updates outside the file save cycle
Fixed tests and updated project references.
Add all folders to the cache dependency (prelim until file watcher work is in)
Updating to release NuGet.config
Merge branch 'release' into dev
Updating to release NuGet.config