Helper library to create pprof-compatible protobuf files

This crate provides an implementation for some common tasks that are usually needed to generate files in pprof's format:

• the module_map crate contains helpers to build the memory map of the profiled process (to populate the mapping field of the Profile) and map each address to the corresponding Mapping (to populate the mapping_id field of a Location).
• the string_table crate contains helpers to deduplicate strings, generate string indices, and populate the string_table field of the Profile accordingly.

In addition, this crate also re-exports all the protobuf type definitions generated by prost.