Misc docs grammar, spelling and capitalization issues

Hi all,

This is my first commit. I hope I've followed the contributions guidelines properly!

I made some changes to fix miscellaneous spelling, grammar and capitalization issues on docs web site.

Here's a link to the commit in my fork:

https://github.com/laran/cassandra/commit/6f738babb1c2d11cc64926e9032db26c03bbdd31

My changes are against trunk.

Thanks!