Mostly const fixes in headers to make it easier for users to have more warnings enabled in static code analysis
Also updating our own rules a bit (kicking some out we won't need yet).
git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6583 dfc29bdd-3216-0410-991c-e03cc46cb475
Usually something like __IRR_SOME_GUARD_INCLUDED__ replaced by IRR_SOME_GUARD_INCLUDED.
Removing underscores at the end wasn't necessary, but more symmetric (probably the reason they got added there as well).
While this touches every header it shouldn't affect users (I hope).
Also a few whitespace changes to unify whitespace usage a bit.
And a bunch of spelling fixes in comments.
git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6252 dfc29bdd-3216-0410-991c-e03cc46cb475