exit(1) and print error messages at the end of program if there's an error

[bact]

• Make LogCountingHandler stores error messages for later use
• Add LogCountingHandler to mdparsing.py, model.py, and rdf.py
• After the generation in main.py, print error messages and exit(1) if there is an error

To resolve #80

The error messages will look like this:

Markdown parsing errors: 1
1: Single list parsing error in line `- file The file represents a single file (default).'

Model errors: 3
2: In class /AI/AIPackage, property autonomyType has type /Core/PresenceType but the range of /AI/autonomyType is /Core/PrssesenceType
3: In class /Software/ContentIdentifier, property contentIdentifierType has type ContentIdentierType but the range of /Software/contentIdentifierType is ContentIdentifierType
4: In class /Software/ContentIdentifier, property contentIdentifierValue has type xsd:anURI but the range of /Software/contentIdentifierValue is xsd:anyURI

Total errors: 4

[JPEWdev]

I have some comments on this, but I'm away from my computer to do a proper review, but I'll look at it later

[zvr]

I am also away this week, so I can't comment extensively, but I disagree with this PR.

• There is on need to add the handling to other loggers, since it should be inherited from the parent one.
• There is no point in collecting the error messages instead of printing them.
• Keep in mind that the error handling will be changed significantly, so that, for example, errors in parsing actually report files and section where the error was encountered. I plan to submit this PR next week (already implemented).