Flag feature

[saracalihan]

we need to flags like global, multiline, case insensitive, etc.

Suggestion:

// STRUCTURE
typedef struct{
  bool global;                  // true 
  bool multiline;             // false
  bool case_insentive;   // true
} CegexFlag;

// USAGE

// use default flags
ceget_match(..., ..., NULL)

// Custom flags
CegexFlag flag = {
  .global=true
};
ceget_match(..., ..., &flag)