Cleanup documentation of coding styles
Currently our coding style documentation is in a relatively messy state.
- It's (nearly) invisible: (I only found this via grep): Documentations->Guides->Whitespace hook->broken link to Codings styles
- White space rules are part of the coding style and should probably be in the same document.
- The prominent discussion of the whitespace transformations during the svn->git transition should be dropped (or moved to "The dune chronicle" page)