New protocol decoder: parallel

libsigrokdecode now supports a new protocol decoder (PD) named parallel.

This PD can decode various simple synchronous, parallel buses that have one clock line and a (pretty much) arbitrary number of data lines.

The decoder can be configured to sample the data lines (e.g. D0-D3 for a 4-bit sync parallel bus, D0-D7 for an 8-bit bus, or D0-D31 for a 32-bit bus, and so on) on either the rising or falling clock edge.

It can then print the data in various formats (currently only 'hex' is supported, but more can be added easily), e.g. 0x55 for an 8-bit bus or 0x55667788 for a 32-bit bus, and so on.