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.
by the PlaceholderParser.
Namely, all the options with the "ratio_over" reference are now handled
correctly by the PlaceholderParser with the exception
of the "first_layer_extrusion_width", which overrides speed of extrusions
by their respective extrusion type.
Also the various extrusion widths (extrusion_width, first_layer_extrusion_width,
external_perimeter_extrusion_width etc.) produce the same numbers
as if ran through the back-end, with the assumption of not overriding
layer height by the variable layer height editing tool or layer height
modifiers.
when parsing localized file names by the PlaceholderParser:
UTF8 characters were handled as chars, and the negative char values were
used as indices into 7bit long tables.
template.
Reworked naming of the plater exports to not use the output file name
template, but to derive the file name from the first printable object's name.
Fixed error handling: Reimpemented the Perl's "eval" blocks
as try / catch blocks.
