Minor documentation corrections before release 0.5.0
Create an example input for common cause failure analysis.

Two train system input is chosen for analysis.
Add a table of contents into the readme file.
[skip ci]
Setup initial code for Common Cause Failure groups.
Add descriptions and classes for all the CCF models.
Add constructors and validators for CCF models.
Add initial Beta CCF model application code without probability
information.

The calculation of probabilities requires numerical operation
expressions because factors and total probability are expressions.
Add Neg numerical expression.
Add "ADD" expression for numerical operations.
Introduce Sub subtraction numerical expression.
Add Mul multiplication numerical operation expression.
Introduce "Div" division numerical operation expression.

Special cases of finding minimum and maximum cases are considered
for multiplication and division operations.
Update documentation and helper scripts with CCF information.
Setup a structure for processing CCF groups from XML input files.
Implement CCF group member addition from XML input files.
Implement factor addition to CCF groups from XML input files.
Add validation of CCF group initialization.
Introduce post-initialization global set-up for analysis.

The new step configures the analysis entities according to the provided
input information. CCF groups are applied, and fault trees are
configured accordingly.
Include the replacement CCF gate in a corresponding basic event.

Now basic events are aware if they are in a CCF group or not. Currently,
basic events do not know which CCF group they are in, but they have only
replacement gate for analysis.
Make fault trees gather information about basic events of CCF groups.

Fault trees provide CCF basic events that are in their structure.
CCF generated basic events are included in general directories, assuming
that CCF analysis is the default behavior.