at the placeholder parser.
Implemented a new PlaceholderParser::evaluate_boolean_expression()
functionality to evaluate just a boolean expression using the full
expressive power of the macro processing syntax. This function
will now be used for deciding, which print or filament preset
is compatible with which printer preset.
The PlaceholderParser is currently used by the GCode.cpp
and by Printer.cpp to generate a new name for the exported G-code or SVG file.
The PlaceholderParser::process() will throw a runtime_error with
a comprehensive error message.
The G-code export will include these error messages into the G-code text
with !!!!!! separators, and the GUI will inform the user, that the G-code
export failed.
https://github.com/prusa3d/Slic3r/issues/443
Change of the PlaceholderParser:
All vector configuration values stored into the PlaceholderParser
are expected to be addressed by the extruder ID, therefore
if a vector configuration value is addressed without an index,
a current extruder ID is used.
Also a small fix of fan handling: The fan speed is set to zero
at the start of the G-code if the cooling for the initial extruder
is disabled.
