backslash is not correctly escaped in string constants

[mikucionisaau]

The issue is specific to Windows where some users prefer to use backslashes in their paths, like "path\\table.csv" where \ is escaped with another \, but Uppaal interprets it like "path\ able.csv", i.e. the second \ sticks to t and results in a tab character instead of a single \.

To reproduce:

• Build libtable-dbg
• Create a model which loads the libtable-dbg and tries to read a file.
• Observe the paths in the error.log

Originally reported: UPPAALModelChecker/UPPAAL-Meta#207