Highlight MQL syntax as C

Taken from http://docs.mql4.com/basis/syntax:

>Syntax of MQL4 is much a C-like syntax

Just for reference, here is a MQL file on Github without highlight:

https://github.com/sergeylukin/mql4-mysql/blob/master/src/mql4-mysql.mqh

and here is C lexer applied to an MQL file (see "How to use" section):

https://github.com/sergeylukin/mql4-mysql/blob/master/README.md