v3.1.0-RC2

This release candidate contains a Style Guide (curtesy of Kevin Townsend) and the following bug fixes:

• Fallback null insertion for autoclonetype (#801)
  If autoclonetype is unable to determine an outer class, this attempts to insert a null (and give a deprecation warning), preserving old behavior (in some cases) where the new behavior doesn't work.
• Fix SyncReadMem.read; add test (#796)
  SyncReadMem.read with an enable signal currently only works in compatibility mode, where Wires are implicitly initialized to DontCare. Fix by explicitly assigning DontCare to the Wire.
• Stricter updateBundleStack - addresses #792 (#793)