Use non-breaking spaces in tables

I have noticed we could improve readability in the RPC tables by using non-breaking spaces in some cases. See screenshot below.

In case you'd like to apply this change separately, here are the sed commands used to replace spaces:
find _includes -type f | xargs sed -i 's/(\([a-z0-9]\+\) or \([a-z0-9]\+\))/(\1 or \2)/g'
find _includes -type f | xargs sed -i 's/(exactly \([0-9]\+\))/(exactly \1)/gi'

![capture du 2014-12-29 19 26 22](https://cloud.githubusercontent.com/assets/3578089/5574568/e87f6662-8f90-11e4-9d4c-0cf15c92a2ad.png)