fix various doc typos in base.rst

I only spotted "reproducable", ispell the rest. 
I also started changing all occurrences of "boolean" to "Boolean", following ispell suggestions (that's also how it is often written in publications, and cf. http://english.stackexchange.com/questions/4481/should-the-word-boolean-be-capitalized). But I stopped half-way because it occurs a lot in the docs and I thought it could be controversial, and surely simpler to leave it as is. If asked, I will continue this change too.