Update the README.

It turns out the new package structure breaks the old import logic
(which sucks IMO, but I'll fix it with care).
Fix a bunch of bugs in the `cwrite` module.

We had problems with format parameters dispatching (`cwritefln` ended up
calling `format` with '\n' as a trailing - orphan - format parameter),
`format` not being imported from `std.string` and an infinitely
recursive template case for the overloaded `cwritef` function.

This also bumps the version to 0.2.1.