Better error messages for Parser and Scanner

[MartinHelmut]

Scanning and Parsing the command line arguments should return descriptive, helpful errors for a user. The current errors are vague and sometimes not explicit enough.

[MartinHelmut]

This needs also be applied to the script parser.

[MartinHelmut]

Following changes to errors are made:

• Show file in which the error happens
• Combine multiple errors in formatting
• Use ASCII chars for better visuals
• I've also added better error messages

This is then how it now looks like (without colouring):

Error: Parameter format is wrong!
  → /Users/martin/Projects/krieselreihe/litr/litr.toml
12 | [params.targete]
   | └─ You're missing the "description" field.
 ...
13 | shortcut = 12
   |          └─ A "shortcut" can only be a string.