Allow compiling of multiple files

New usage:
:make src/filename1.erl src/filename2.erl escript.erl

Notes:
 * Does NOT automatically include the current file.
 * Does NOT allow patterns (such as src/*.erl) or directories.
 * Exit status is 1 when an error is found.
Use location lists

 * Use lmake instead of make on BufWritePost
 * Signs persist for all files until errors are fixed
Merge pull request #4 from fishcakez/location_list

Use location lists instead of quickfix lists