Simplify probability analysis code.
Introduction of indexed fault tree and gates.
Fix XOR and negative events related logic in analysis.
House events are not reported in probability and minimal cut sets.
Fixes #80.
House events are treated as constants and removed from
minimal cut sets.
Closes #81.
Recover ThreeMotor tests.
Add simple test for Atleast gate.
Cleanup fault tree analysis class.
Direct assignment of basic event container in probability analysis.
Introduce importance analysis: DIF, MIF, CIF, RRW, RAW.
Closes #75, closes #76, closes #77, closes #78, closes #79
Better formatting for output of importance calculations.
Documentation update about importance calculations.
Support for multiple input files with fault trees and model data.
Closes #83
Add high probability events in Chinese input file.
Report importance factors only for basic events in minimal cut sets.
Closes #82
Change probability calculation algorithm.

The equation is now expanded as in uncertainty analysis. This may lead
to merge of these two types of analysis.
Add mcs input for Chinese tree.
Remove coherency specific methods in probability calculations.
Simplify uncertainty analysis class.

Uncertainty analysis class privately inherits from probability analysis
class and uses functions and protected members for its own operations.
Fix the MCUB and rare event approximations for importance
calculations.
Fixes #84