Clearer parsing errors

[Stefan Pfenninger]

Problem description

On encountering parsing errors with pyparsing we should print out only:

1. The expression in which the error occurs
2. The error message
3. The location (char / column number)

If possible, we could draw a character to highlight the location in the expression (1).

Calliope version

0.7

[Bryn Pickering]

Fixed in #436