extopts: Removed getopt-compatible form.

Main reason is to get simplier for understanding library. It is not
too much for ask to learn extopts way of working.
extopts: Code usage corrections.

* added separate macros for aiding in structures composing;
* flag variable of non-argumental parameters changed from char to int
  variable;
* renamed extarg_type enum;
* some cosmetic changes.
extopts: Fix for short options parsing.
extopts: Code refactoring.

Function get_extopt() is separated into different subfunctions.
Added error handling for parameter argument parsing fail.
Fixed memory leakage of longopts array.
extopts: Main parsing function removed to get_extopts.

Since unlike standart getopt_long() it processes all command line
arguments in single call it looks to be more proper to call function
in new way.
extopts: Cleaning all no-argument parameters flags before parsing
command line just to be sure.
extopts: Added check in integer arguments parsing.
extopts: Implemented allocated string argument type.

Such strings should be allocated before they are passed to extopts (in
form of char* instead of char** for simple string type).

After command line parsing such string arguments can be modified.
extopts: Basic string argument type is protected by const.

Now handling of string parameters is handled thoutgh 'const_str'
instead of 'addr' field of extopt structure. So EXTOPT_ARG_STR awaits
now 'const char **' instead of 'char **'.

This protects from using STR type for reading string argument and than
changing it while it is still located at command line arguments
string.

If changing is needed then STR_ALLOC type should be used or STR but
the contents of it must be copied to other location.

BE AWARE not to use 'addr' field for this type of arguments since in
this case it will not help you to track down if you accidentally
defined string as non-const and than also accidentally writing into
it. It is better to simply do not show off and use EXTOPT_ARG_STR
macro :3
extopts: Added runtime extopts validation in get_extopts function.