Rework of the JSON schema

The main modification in this release is a reworking of the schema to make the JSON file easier to parse and work with, in particular for statically typed languages (see #1). Other modifications:

• Microarchitectures in the ppc64 or ppc64le family can be queried for vsx and fma instructions
• Version suffixes for compilers have been abandoned as a way to distinguish among them. Apple's clang is now called apple-clang in the JSON file