Improvements on UTF-8 and handler functions
1. Code refactored for easily adding of string handlers and it's arguments into $map array;
2. Made adjustments that all default text is under UTF-8 encoding.
Fixes and improvements
1. Typo fixes;
2. Added base64-related operation;
3. Changed way of numeration of operation options. Now all options have unique index to avoid of interfering of submit results;
4. Changed names of constants to avoid spelling errors in PhpStorm.