Riscv-config

Changed
- default mpp value to 0
- adding defaults to sub-fields of mtvec

Added
- Added support for pmp csrs in the schema
- Added support for mcycleh and minstreth
- Added special checks for ensuring the shadows are implemented correctly.
- Added support for the following supervisor csrs in the schema: sstatus, sie, sip, stvec, sepc, stval, scause and satp
- Added support for user performance counters, frm, fcsr, time[h], cycle[h] and instret[h] csrs in
the schema.
Changed
- all fields are now subsumed under a hartid. This allows specifying multiple harts in the same
yaml
- logging mechanism improved.
- isa spec is now validated independently of the platform spec
- privilege and unprivilege version checks are no longer required. This satisfied via the
"allowed" field now.
- improved the 'implemented/accessible' checks for s, u and n extensions
- the "fields" node is now populated by subfields in the increasing order of the placement in the
csr.
- using aliases to reduce the code size

Changed
- Added Zihintpause to ISA string (for PAUSE Hint instruction extension)..

Changed
- Size of the isa schema has been reduced significantly.
- Using anchors in the schema.
- Provided a command line argument to disable anchors in the checked yaml dump.
- adding mycycle, minstret, pmpcfgs and pmpaddrs
- added support for defining multiple harts

Changed
- Changed quickstart 'riscv_config' to 'riscv-config'
- Changed checker.py to add check_reset_fill_fields() description

Changed
- Changed minimum python version requirement to 3.6.0 which is typically easy to install on all
major distributions
- Updated readme with better installation instructions