Ninja backend: objects generated with custom_target can be linked
Pass -qt5 command line argument to qt5 tools because otherwise they fail on Debian systems where qt5-default is not installed (e.g. pbuilder).
Merge pull request #15 from osimola/custom_object

Detect object files generated by custom targets and add them to the link.
Added attribution.
Removed -qt5 arg as that should be handled elsewhere.
Use correct path when installing headers. Fixes #16.
Can install man files from a subdir.
Can install data files from subdirectories.
Can install entire subtrees with one command. Closes #14.
Implement a foreach loop construct. Closes #17.
Dafuq?
Pkg-config detection cleanup.
Harmonise held_object usage somewhat.
Further harmonise held_object.
Minor tweak.
Do not quote $out or $in because Ninja does it by itself.
Allow getting builtin options with get_option. Fixes #23.
Add number, string and array arithmetic

Addition (+), subtraction (-), multiplication (*) and division (/) for numbers
follows the BIDMAS rules.

Strings and arrays can be concatenated with the addition operator

Strings can be concatenated with numbers with the addition operator
Create symlinks properly. Fixes #19.
Signal handling for run_tests.py

SIGINT and SIGTERM are handled, causing further test execution to stop and
the results to be printed immediately. Also cleans up prebuilt objects