iCalendar feed validation

As part of the debugging process that resulted in [the BP Docs conflict](https://github.com/boonebgorges/buddypress-docs/issues/425) I posted on that repo earlier, I initially thought that empty calendars I was seeing may have been to result of the iCalendar template output. I discovered that the iCal feed template does indeed produce output that does not validate, as perhaps suggested by [this comment](https://github.com/stephenharris/Event-Organiser/commit/665881b7e35c59ae45a6dfed17d568ec112827f8#commitcomment-3783835) on the initial commit.

IIRC, the issues with it were:

* Every line must end with `CRLF`
* The `ORGANIZER` token needs to be of the form `ORGANIZER;CN="John Smith":MAILTO:jsmith@host.com`
* "folded" lines had extra whitespace which caused anything after the break to be parsed as a token

Er, I think that was it...