This interface provides some convenience functions for mapping
opaque record identifiers (could be a filename, file descriptor,
or any other type of file handle) to a corresponding runtime
structure referencing the actual file record. This runtime
structure should at least contain a pointer to the actual file
record, and can also persist arbitrary state for this record.

- memory management is now entirely handled by darshan-core for
  module records
    * when registering new records, darshan-core returns the
      corresponding buffer to write it to, rather than allowing
      module to determine this
- modules now decide whether darshan-core should track record
  names by passing either a valid name or NULL to the register
  function
    * this allows modules to register records that aren't really
      tracked by darshan-core
- only the POSIX module has been ported to new changes for this
  commit

also some code clean up to change references of record hash
to name hash to be more clear about what it is actually storing.

epilog will now skip on-node compression if only a single compute
node is used and will generate the final log file instead

dev-modular should be completely merged into mmap-dev branch

- modules now receive a memory buffer after successfully
registering with darshan-core. modules can request a specific
memory amount, but may not be honored depending on the configured
darshan memory limit
- split the previous register_record function into 2 parts:
    * lookup() -> lookup darshan_record_id corresp. to path name
    * register() -> register record_id & name with darshan-core
- register_record now returns true if the record added; false
otherwise (if module was out of memory or darshan is out of memory
for storing id->name mappings)

Now, register_record() accepts an argument for the size of
the record being registered, and this is used to track how much
data each module has stored in their allocated memory region.

Now, as the app executes, darshan-core persists the id->name
mapping data to the tmp log file. This is done by serializing the
id->name mapping to the mmap log file region when new records are
registered.

user can now give a config option or use a runtime environment
variable to control darshan's per module memory requirements.

this indicates whether the log file is complete or only partially
written

* header is now raw uncompressed, rather than gzip format
* mapping info stored in header is now in uncompressed terms
* storing mapping info for job data now