Updating the host docs to reflect v5 changes.

Also pulled the assembly scanning info into a seprate doc.
Fixed a few spelling mistakes
Clarified which assemblies get included by default
Fixed typos and clarified the assembly scanning process.
Adding asm scanning to TOC
Added code snippet for v5 endpoint customization and moved the nsb v3 and v4 section for customization above logging.
Included the v5 suffix for the AsAClientEquivalent snippet.
Merge pull request #490 from Particular/updated-host-docs

Updating the host docs to reflect v5 changes.