English corrections and typos

This commit consists mostly of rewriting some passages of the website
that where either gramatically incorrect or that lacked a little bit of
"english style"
There as also been various typos and such.
I tried to stick as much as possible to the initial idea/"way of saying
it", but I might have misunderstood in some cases the real meaning, so
this should require some checking...
Merge pull request #1 from zwindler/zwindler_eng

English corrections and typos