* CallGraph, VariableVisitor: unify visit arguments behaviour to avoid lookup errors of calls
  by the CallGraph that were not registered by VariableVisitor.

Add CI tests on merge

See merge request !44

Implement criterion which don't need a file.

See merge request !43

Add module-info.java to sdg-core

See merge request !42

The PPDG makes some transitive CDs direct, in order to
remove some of them. The ES-SDG then stops some of these,
which had the consequence of not reaching `Enter` in some
cases.

* Removed null pointer when type is not specified
* Improved usage message
* Clarified error messages

# Conflicts:
#	sdg-core/src/main/java/tfm/graphs/CallGraph.java
#	sdg-core/src/main/java/tfm/graphs/cfg/CFGBuilder.java
#	sdg-core/src/main/java/tfm/graphs/sdg/MethodCallReplacerVisitor.java
#	sdg-core/src/main/java/tfm/graphs/sdg/SDG.java
#	sdg-core/src/main/java/tfm/graphs/sdg/sumarcs/NaiveSummaryArcsBuilder.java
#	sdg-core/src/main/java/tfm/nodes/type/NodeType.java

Removed WIP and development guidelines.

* Migrated `NodeType`s to specific `GraphNode` child classes.
* Revamped creation of SDG
* Added ASDG and PSDG, based on the APDG and PPDG.
* Improved handling of variable usages, definitions and declarations.
* Added movable variable actions, that can be placed in a CFG node and
  then relocated to their own PDG node.
* Added fix-point and specific slicing algorithm to summary arc
  generation.
* Documentation of most methods (public and private).
* Removed unused elements.
* Fix possible errors by migrating all maps whose key is an AST node
  to IdentityHashMap.