Add class for calculating shortest paths using GH.
Make ST_ShortestPath support unweighted graphs.
Modify the tests for ST_ShortestPath.
Update debugging output of ST_ShortestPath.
Add method for printing a DiskBufferDriver.
Merge branch 'GH' into shortestPath
Refactor SP String messages into local fields.
Merge branch 'GH' into shortestPath
Refactor SP String messages into local fields.
Adjust description of ST_ShortestPath.
Merge branch 'refactor' into shortestPath

Conflicts:
	src/main/java/org/gdms/gdmstopology/function/ST_ShortestPath.java
Update javadoc.
Refactor closeness String msgs into local fields.
Refactor ShortestPath function description.
Merge branch 'refactor' into shortestPath

Conflicts:
	src/main/java/org/gdms/gdmstopology/function/ST_ClosenessCentrality.java
	src/main/java/org/gdms/gdmstopology/function/ST_ShortestPath.java