Detect functions and constants heuristically

[msjyoo]

For example, if a constant is in all upper case letters, then there should be an option to consider it as a constant and apply syntax to it accordingly.

Similarly to functions e.g. func( with bracket could be considered a function (phpUserFunc and phpUserConst)?

[VonHeikemen]

Using the syntax override method suggested on the readme, one could do this to highlight function calls.

function! PhpSyntaxOverride()
  syn match phpFunctionCall /\v\h\w*\ze(\s?\()/ 
    \ containedin=phpRegion,phpIdentifier

endfunction

augroup phpSyntaxOverride
  autocmd!
  autocmd FileType php call PhpSyntaxOverride()
augroup END

I'm sure there is a better way to do it inside the plugin itself.