Rearrange ClietMessageData creation test params

This isn't strictly necessary, but the test didn't match how one would actually
create a ClientMessageEvent. This test fixes that.
xcb enums are 0-based
Correctly render enums with explicit values in the middle

It looks like someone at some point between 1.7 and 1.10 made all of these
explicit (i.e. they have an explicit value parameter for each value, not just
some of them). However, it is still a bug in the places where people didn't do
this, and also if people are trying to use xcffibgen on xcb-protos < 1.10.
Add more tests for a strange enum in 1.7
Release v0.1.8
All X11 events are 32 bytes long

All X11 events in wire format are at least 32 bytes long, so we should encode
them as such. Fucking X :(

Closes #31