VPTOOL: Switch to Yaml storage infrastructure. Improve consistency of ISA_RV32 database.

Created by: zchamski

This PR converts VPTOOL to use Yaml-based persistent storage and improves the consistency of the ISA_RV32 database which contained duplicate item tags.

• By default, VPTOOL now uses Yaml databases for input as well as output.
• It is possible to convert existing Pickle databases to Yaml format.
• The existing databases present on the cva6/dev branch were converted to Yaml and sanitized:
  • Duplicate tags in ISA_RV32 database were replaced by unique tags based on individual feature IDs;
  • The name of the 32-bits ISA project was changed from ISA to ISA_RV32 to match the database directory name and to avoid future ambiguities (including tag naming).

The Yaml import/export interface uses a so-called "round-trip" parser which preserves the formatting of the database files upon parsing (loading) the database and restores the formatting upon unparsing (saving) the database. Any comments found in the input database will be preserved and restored when saving the output database.