This marks BOOM version 2.2.0.

Changes:

• All configurations now support RISC-V compressed ("RVC") instructions
• PMP registers are enabled
• The NBDCache has been forked from rocket-chip
• Minor CSR instruction fixes
• ReadTheDocs documentation available at https://docs.boom-core.org/en/latest/
• CircleCI continuous integration
• Switch to Chisel3 syntax
• Updates for September 2018 rocket-chip

This version should be used with the following commit of rocket-chip (from the master branch): https://github.com/freechipsproject/rocket-chip/commit/50bb13d7887e5f9ca192431234b057ae9d8edb6c

This version should be used with the following commit of boom-template (from the master branch): https://github.com/esperantotech/boom-template/commit/1a0f9557f11d32f155ac17b9e3d4700d1dd69ad9