Sample only probabilities of basic events in minimal cut sets.
Introduce earlier detection of invalid values for sampling.
Fix tests for expressions.
Simplify indexed fault tree.

Refactoring function signatures to reduce the number of containers
to be stored with indexed fault tree.
Simplify ExpandSets method in fault tree analysis.
Initial sketches for in-fault-tree expansion of gates for
minimal cut set finding.
Minor documentation update.
Introduce basic logging system for use in debugging.
Closes #85
Simplify gate expansion by propagating complements.

Complements are propagated in pre-processing stage, so
no negative gates are expected in expansion stage.
Add new inputs to show if De Morgan's Law is handled.
Simplify Superset class to handle only positive gates.
Re-work for removal of house events from fault trees.
Introduction of minimal cut set analysis in indexed fault tree.
Bug fixes for nulled sets in indexed fault tree.

There is a memory leak in the analysis, which is evident on 200 event
tree.
Remove the previous core code for minimal cut set finding.
Re-introduction of limit order for cut set generation.

Currently this implementation is not fully working. There seem to issues
with consistent results.
Remove unnecessary GoogleTest files.

Some compiler and builder specific files are removed. In case they are
needed, they can be download from the trunk.
Suppress 200 event tests due to current memory leak.
Merge branch 'develop' into coverity-scan

Conflicts:
	.travis.yml
	README.rst
	doc/opsa_support.rst
	doc/speedlog.txt
	doc/todo.rst
	tests/input/fta/correct_expressions.xml