add convolution generators to libosmocore
There's general framework for convolution generators in libosmocore but to actually be useful it requires state tables, puncturing scheme etc. Right now there is some code in osmo-bts and in libosmocore's tests.
As it would be generally useful (for instance gprs debugging), we should cleanup that code and expose it as osmo_* functions which can be shared by all projects.
Ideally, generator for state tables should be added as well with extensive documentation to simplify further expansion.