Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=2059

Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=2024

Avoids the clutter and maintenance effort associated with providing the
function signature string.

This reverts commit c5bea524.

This reverts commit b18f6cc1.

- mapFields and splitMeshRegions need more clarification

- operator[] with label -> get args at index
- operator[] with word  -> get named option

- ensure that the standard options (eg, from timeSelector) also have
  some usage information

- markup codingStyleGuide.org examples so they actually indent correctly

- use 'Info<<' as per codingStyleGuide instead of 'Info <<'

the include file back to mathematicalConstants.H to make upgrading code slightly easier.

- also drop various unused time options from src/OpenFOAM/include

- change system/controlDict to use functions {..} instead of functions (..);
  * This is internally more efficient
- fixed formatting of system/controlDict functions entry

- pedantic change: use 'return 0' instead of 'return(0)' in the applications,
  since return is a C/C++ keyword, not a function.

- can use 'XX.empty()' instead of 'XX.size() == 0', 'XX.size() < 1' or
  'XX.size() <= 0' or for simpler coding.
  It also has the same number of characters as '!XX.size()' and /might/ be
  more readable

- many size checking had 'XX.size() > 0', 'XX.size() != 0', or 'XX.size() >= 1'
  when a simple 'XX.size()' suffices