Improving Reference/index's grammar

This change fixes typos and improves the grammar of the
Reference/index.md text. (Example: "Umbraco" is a proper noun and thus
should be capitalized.)
Improving Reference/index grammar Part 2
Improving Documentation/index's grammar

Simple grammatical improvements, such as capitalizing "Umbraco."
Improving Installation/index's grammar
Improving Install-Umbraco-Manually's grammar.
Merge pull request #123 from brentmiller/master

Improving text grammar and style