Implements #4048#7196
Syntax:
(global|local) variable_name =
(scalar_expression|vector_variable|array_expr|initializer_list)
array_expr := array(repeat, value)
initializer_list := (value, value, value, ...)
The type of the newly created variable is defined by the type
of the right hand side intitializer.
Newly declared variable must not override an existing variable.
Variable may be assigned with global|local expression, but its type
must not be changed.
Newly the assignment operator also accepts the same right hand expressions
as the global|local variable definition.
1) Implemented access to coEnum values, they are returned as strings.
2) Fixed some possible memory leaks.
3) Fixed some possible union type punning issues.
The thread local storage variables for the random number generator
were replaced by an external context variable.
Thread local storage is a scarce resource.
Errors in the file output templates are reported in mono-spaced font,
so that the arrow character ^ is displayed at the right column
pointing to the offending spot.
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.
from the current Model/ModelObjects.
Fixed a possible race condition in updating Print::m_placeholder_parser
with the proposed filename / filename base.
Improved documentation (source code comments).
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.
