First cut at dSYM support

[fosterbrereton]

As noted in one of the PR's comments, this PR makes a lot of assumptions about the various files, nuances, metadata, directory structures, etc., that are contained within a dSYM directory. I would expect further tweaks will be necessary as real-world issues are found. Until then, this appears to do things.

To make a dSYM from a binary, use dsymutil (docs):

cd /path/to/binary
dsymutil binary

This will create binary.dSYM next to the binary. Note: when passing a dSYM folder to orc, you must omit the / at the end of the path, or orc will pass it over:

./orc /path/to/binary.dSYM # ok
./orc /path/to/binary.dSYM/ # error

You can also create a "flat" symbol file which ORC also supports with this PR:

cd /path/to/binary
dsymutil binary --flat

This will create binary.dwarf next to the binary.

In either case, dsymutil does not modify the binary (you'd use strip for that).

This PR also adds a couple tests to ensure ORC scans the two file formats above successfully. It does this by making dSYMs from its own debug binary, and scans them.

[leethomason]

Good start