Merge JVM and KLib ABI dumps into a single file

[fzhinkin]

Currently, JVM and KLib dumps are generated and stored separately.

It could be confusing for libraries authors, especially because neither of these two dumps cross-refer to another one (i.e. by looking at a klib dump, one may get an impression that there are all sorts of targets, but JVM).

Possibility of merging these two types of dumps together should considered. If it's impossible, then docs might need to be improved to better reflect why there are two distinct dumps. Also, if comments inside the dumps (see #230) will be supported, we can include corresponding info using it.