Add support for parsing arrays of hashes.

See https://github.com/mojombo/toml/pull/153.
Add helper get_as function.
Add function to get a toml_group_array from a toml_group.
const correctness fixes for get_group() and get_group_array()
Merge branch 'master' into array-of-hashes
Add convenience function for inserting simple values.
Inline keygroup array printing function.

Clean up a few comments as well.
Merge branch 'master' into array-of-hashes

Conflicts:
	include/cpptoml.h
Fix trailing whitespace (array-of-hashes).
Merge branch 'master' into array-of-hashes
Remove stray merge line.
Merge branch 'master' into array-of-hashes
Merge branch 'master' into array-of-hashes