lines2insns: Implemented basic searching for insns (no filtering yet)

The tool now finds the instructions corresponding to the input source
lines and outputs their locations to stdout.

A few important things are not yet implemented though:
* output the offset into the "init" or "core" area and output it
  instead of the offset in the current ELF section;
* filter out the insns that do not access memory;
* if requested, filter out %rsp/%esp-based accessed and locked ops.