Issue #4: Flymake support - on-the-fly compilation

[danmey]

Please see initial on-the-fly compilation support via. flymake.

Few notes:

• it does not need any external script as other solutions to overcome single line diagnostics parsing in flymake
• it uses ocamlbuild as a backend. This choice is pragmatic - it has the biggest chances to build the file, even when the project is not using it
• as ocamlbuild needs to be invoked on root of project, the root is where the .typerex file is located
• consider using flymake-cursor to show the diagnostics in mode-line
• consider integration with ocp-ocamlc tools, that means life update of the .cmt files !