Follow variables naming convension
Functions use the same argIndex for designating derivative argument as their caller function
Issue a warning when trying to derive a function with no parameters.
Synchronize test messages with the Diagnostics system.
Update derivative argument designtion. It is updated in correspondence of the newer version of llvm and clang. Added test messages.
Surround function names with ticks
Merge pull request #3 from mvassilev/master

Identifier name changes. Correct argIndex usage of callee functions.