FuseSoC integration

1. FuseSOC asks LibreCores for the VLNV(Vendor Library Name Version) for example, wallento:arbiter:rr:1.5
2. LibreCores replies with provider information, i.e. a URL to the .core file (for example, https://github.com/wallento/fusesoc_cores/blob/master/cores/arbiter/arb_rr.core)
3. FuseSOC caches the core in the local librecores library cache and writes the provider information to the provider file.
4. FuseSOC now has all it needs to fetch the core source code into the core cache