Initial docs

[SK1Y101]

Features:

• changelog and nox environment to build it
• handling of skiylia version at command line 'skiylia -v'
• a skiylia highlighter-parser

Bugs:

• debug level forced to 2 in testing environment
• versioning information stored as class

Documentation:

• better usage and installation section
• introduced new whats new area as a human-edited version of the changelog.

Tests:

• test_skiylia now includes versioning checking