1) Starting with this commit, configuration block exported into G-code
is delimited by "; prusaslicer_config = begin" and "; prusaslicer_config = end".
These delimiters look like any other key / value configuration pairs
on purpose to be compatible with older PrusaSlicer config parsing from G-code.
2) Config parser from G-code newly searches for "; generated by ..."
comment over the complete G-code, thus it is compatible with various
post processing scripts extending the G-code at the start.
3) Config parser from G-code parses PrusaSlicer version from
the "; generated by PrusaSlicer ...." header and if the G-code was
generated by PrusaSlicer 2.4.0-alpha0 and newer, it expects that
the G-code already contains the "; prusaslicer_config = begin / end"
tags and it relies on these tags to extract configuration.
4) A new simple and robust parser was written for reading project configuration
from 3MF / AMF, while a heuristic parser to read config from G-code located
at the end of the G-code file was used before.
1) All slicer's exceptions are now derived from Slic3r::Exception.
2) New exceptions are defined for slicing errors.
3) Exceptions are propagated to the Plater to show.
It remains to modify the slicing back-end to throw the new SlicingError
exceptions instead of std::runtime_error and to show the other exceptions
by a message dialog instead of a notification.
A static symbol Slic3r::SEMVER is introduced, which holds
the running slicer's Semver object.
This is mainly done to make testing updater behaviour
_much_ easier. Additionaly to cleanup some questionable code
(Semver was being parsed multiple times / in multiple places
in the frontend.)
