Merge pull request #1 from jrhoads/master

Add a requirements.txt file
strip out any empty data values, so we don't put empty xml tags in the mods
add originInfo place handling
Merge branch 'master' of https://github.com/Brown-University-Library/mods_generator
add originInfo publisher handling
start work on allowing data part separators to be escaped
finish work on allowing data division separators to be escaped
don't force the spreadsheet to escape section separators if there are no sections in the mods location field
better title handling
allow mods ID attribute to be set
add another possible name for the id column
re-work the file-naming a bit
add function to get the column with data filename(s)
get ModsRecord objects from DataHandler, instead of clients needing to know so much about the DataHandler class
add support for a list of data_files to ModsRecord
add support for <mods:subject><mods:temporal>
add support for <mods:physicalDescription><mods:note>
add another id col name
only copy parent mods into children if we explicitly ask it to
fix subject topic/temporal handling to accept list of topics or temporals