[Lazarus] Wiki page "Unicode Support in Lazarus" improved

[Juha Manninen]

I have simplified and improved the page
 http://wiki.freepascal.org/Unicode_Support_in_Lazarus

I tried to move relevant information to the top and remove duplicate
information.
For example there is a short "Usage" section with simple rules and then:
 "These rules make most code already compatible with Delphi."
which is pretty much what most people need to know.

Please check.

Juha