A simple C++ command line arguments parser

WIP

1. Create an instance, passing argc and argv directly, like this:

   EasyArgs *ez = new EasyArgs(argc, argv);

   or use the other available constructors:

   EasyArgs(int argc, std::string argv[]);
   EasyArgs(std::vector<std::string> argv);

2. Specify Version/Description (optionaly) for the usage message:

   ez->Version("0.1")
     ->Description("Example");

3. Add Flags:

   ez->Flag("-b", "--bacon", "bacon help message")
     ->Flag("-v", "--verbose", "be verbose");

   Flags are optional arguments given in the form of "-a" (short form) or "--argument" (long form). Multiple flags can also be given in the form of "-abc".

   Flags are considered set (meaning the have a boolean value of true) when they are given in the program's cmdline arguments.

   To get the boolean value use ez->IsSet("--long") or ez->IsSet("-s") (long or short form respectively).

4. Add Values:

   ez->Value("-f", "--foo", "foo help message", true)
     ->Value("-p", "--pizza", "everybody likes pizza", false);

   Values are arguments given in the form of "-a=value" (short form) (short form) or "--argument=value" (long form).

   The 4th argument of the function ez->Value() is a boolean value specifying if they are required of not.

   If required, but not given, an exception is thrown.

   You can get a value from the given args with ez->GetValueFor("--long") or ez->GetValueFor("-s") (long or short form respectively).

   ez->GetValueFor(...) will return an empty string "" if the argument is not given or specified.

5. Add Positional arguments:

   ez->Positional("name", "your name")
     ->Positional("nom", "om nom");

   Positionals args are required. If not given, an exception is thrown.

   To get the value of the positional, use ez->GetPositional("name_of_the_positional").

For the example let's suppose that the program is being run like this:

$ ./my_program -pba -m=12 --foo=bar --verbose pos1 -Sw pos2

int main(int argc, char *argv[])
{
	/* EasyArgs has a contructor for passing directly the cmdline args like this: */
	EasyArgs *ez = new EasyArgs(argc, argv);

	ez->Version("0.1")              // specify version
	  ->Description("Example")      // add a description

	  ->Flag("-b", "--bacon", "bacon help message")        // add some flags
	  ->Flag("-v", "--verbose", "be verbose")
	  
	  ->Value("-f", "--foo", "foo help message", true)     // add expected values (true = required)
	  ->Value("-p", "--pizza", "everybody likes pizza", false)
	  
	  ->Positional("name", "your name")                    // add expected positional
	  ->Positional("nom", "om nom");
	
	//ez->PrintUsage();             // print usage info if you want


	ez->IsSet("-w");                // false because such argument doesn't exist
	ez->IsSet("-S");                // false, for the same reason
	
	ez->IsSet("-b");                // true, because 'b' is set (in the group of "-pba")
	ez->IsSet("--bacon");           // true, --bacon is long form for -b
	
	ez->IsSet("-v");                // true, same with above
	ez->IsSet("--verbose");         // true, same
	
	ez->IsSet("--foo");             // false, --foo is a value arg, not a flag
	ez->IsSet("-f");                // false, same reason

	ez->GetValueFor("--foo");       // "bar"
	ez->GetValueFor("-f");          // "bar"
	
	ez->GetValueFor("-m");          // "", because arg is not specified (even if given in cmdline)
	ez->GetValueFor("-p");          // "", because "-p" is given, but as flag
	ez->GetValueFor("--pizza");     // "", same

	ez->GetPositional("name");      // "pos1", positionals maintain their order, so "pos1"
	ez->GetPositional("nom");       // "pos2", same

	delete ez;

	return 0;
}

With ez->PrintUsage() you can print usage info:

version: 0.1
description: Example
usage: ./my_program [OPTIONS] name nom 

OPTION       REQUIRED   DESCRIPTION
===========================================
-b, --bacon	no	bacon help message
-v, --verbose	no	be verbose
-f=, --foo=	yes	foo help message
-p=, --pizza=	no	everybody likes pizza


POSITIONAL      DESCRIPTION
===========================================
name		your name
nom		om nom