TODO:
- differentation of variables for read and write commands
- help command (printing all commands posibilities with descriptions)
- documentation updated (buffer sized, return enum types, write variable nums, buf size hints)
- helper setters and getters for variables

0.11.0
* optional context in commands and data_getter in variables
* optional extended read and write variable handler with parent command

0.10.1
* single working buffer insteads of two separated for atcmd and unsolicited events

0.10.0
* separate atcmd and unsolicited event state machines

0.9.0
* variables accessors

0.8.1
* fix commands shourtcuts

0.8.0
* print commands list feature

0.7.1
* more flexible command group initialization (pointers)

0.7.0
* function for checking unsolicited buffer
* some refactoring regarding unsolicited buffer
* helper function cat_search_variable_by_name added
* commands group with searching feature added
* disable feature for commands and groups added

0.6.0
* async non blocking io->write
* async unsolicited read/test event (injected at idle and hold state)
* hold commands parse processing feature (for delayed unsolicited read responses)
* behavior differentation by callbacks return values
* only-test flag in commands descriptor (for fast disable read/write/run)
* helper function for searching command by name
* multiple responses triggered by single request pattern support
* generic mutex descriptor interface
* return value states enum types

0.5.3
* function for checking internal busy state added

0.5.2
* small fix in auto description response

0.5.1
* description field in command added (used in auto help message)

0.5.0
* test command parser with auto help messages
* output string end-line encoding same as input string
* very basic demo example application added

0.4.0
* high level parsing for command arguments
* int, uint, hex, hexbuf, string argument types
* validating arguments values range

0.3.0
* independent buffers (parsing buffer and state buffer)

0.2.0
* passing command struct instead of command name in command handlers