Pylsv2

This release adds two new functions:
- get_error_messages() reads all available error messages from the control. Only works for iTNC
- get_file_list(path=None, descend=True, pattern=None) returns a list of all files and applies a regex filter to the file name

With this sphinx is used to generate documentation based on the docstrings.

Integrate 12 to fix problem with not recognizing table names and column titles.

The function get_override_info() was added to read the current values of all three overrides: Spindle, Feed and Rapid

The function `get_spindle_tool_status()` was added to read status information about the tool currently in the spindle. This only works for iTNC530 controls with software version 34049x 04 and 60642x 01. For other controls see [lsv2_demo.py](https://github.com/drunsinn/pyLSV2/blob/d79a106e2a246a76bd4b13c4a6883404af964635/scripts/lsv2_demo.py) on how to read the pocket table to get similar information.

Cleanup and improvements on the file information functions.

This release adds the following new functions:
- send_key_code: Simulate a keypress on the control. only works if you first lock the keyboard access. Available keycodes can be found in const.py
- set_keyboard_access: lock and unlock the keyboard access
- set_machine_parameter: Change the value of a machine parameter
- get_machine_parameter: Read the current value of a machine parameter
- is_itnc, is_tnc and is_pilot: check which type of control to enable workarounds for differences in implementation

Other changes:
- The main class collected a lot of constant definitions. These wer extracted to const.py to clean up the code. They will be removed from the main class in a future release
- Translation from error codes, execution and program state is now handled in translate_messages.py
- updated lsv2_demo.py to show how to use the new functions
- pytest can now run agains TNC640, iTNC530 and CNCPILOT640