New meta parser

To parse options before the actual tests. The options are parsed to a dict and are available in core (so far). The options are intruduced by the OPTIONS: keyword. The tests by the TESTS: kw. If both are missing, we fall back to plain old-style parsing as it was before.

next steps: where to put options?

• i prefere a global dict, like pandas also do
• also merging it with the **kwargs passed to the functions is a possible, but feels a bit clumsy..

example meta.csv:

OPTIONS:
datetimeformat: %d.%m.%Y %H:%M:%S
plot: all

TESTS:
headerout,date start,date end,assign,Flag_1
temp,,,,"range, {min: -15.0, max: 15, plot: True}"
temp,,,,"range, {min: -10.0, max: 10, flag: DOUBTFUL, plot: True}"
temp,,,,"range, {min: -3.0, max: 3, flag: OK, plot: True}"
temp,,,,"generic, {func: ismissing(this), plot: True}"
temp,,,,"range, {min: -30.0, max: 30, plot: True}"