Improved English grammar, wording and spelling

I've just gone through, and generally chaned the parts where it didn't sound like normal English into the wording that would be expected by a native speaker (in this case me - although I work in Marketing, so I should be a pretty good judge of this stuff).

In some cases I had to change the wording quite a bit, to get what I believe the intended meaning was, across. Where this has happened, I've made a comment in the commit description.

In the first file, I needed to add a word with an apostrophe (ie ' symbol). I wasn't sure if this needed to be escaped in XML, so currently it isn't. Please fix if necessary! (I'm a marketer / designer, not a coder. :-)

Hope this helps! I'm looking forward to using OsMo! :)