- you can't search for a year, just individual dates.
- you can only display 100 results at a time.
just use this filter and iterate over the date:
add fields (genre or whatever) to the url as you need them (http://www.giantbomb.com/api/documentation#toc-0-15).
you need to do one query for each date in a year.
if field "number_of_total_results" in the response is >100, do the same query again with added filter "&offset=100". do subsequent queries for that date while "number_of_total_results"-100 is >0. you _probably_ can get by without this whole mechanic as i guess it's unlikely that there's more than 100 releases for any given date, but you be the judge of that.
now you should have queried everything.
as to converting the json data to csv: there's tones of snippets and libraries out there: https://www.google.de/#q=python%20json%20to%20csv
i'm bored, so here's all of this in pseudo code: http://pastebin.com/Y9TBVibz