Simple tool to convert csv into ics.

The tool expects 4 fields in the csv:

 * summary -- short blurb
 * description -- longer text
 * start -- start date
 * end -- end date

The date has 2 potential formats:

 * %a %b %d %Y e.g. Mon Jan 18 2016
 * %a %b %d %H:%M %Y e.g. Mon Jan 18 14:35 2016

You can hack up `mk_time()` if you need other formats.