documentation: Replace project name with Vectorscan and general updates

documentation: Replace project name with Vectorscan and general updates

The generated documentation continues to refer to Hyperscan
despite the project now being VectorScan. Lets replace many
of the Hyperscan references with Vectorscan.

At the same time, lets resync the documentation here with the
vectorscan readme. This updates the supported platforms/compilers
and build options.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>