OffsetCurve function
Improve OffsetCurve signature
Fix test
Merge irstv/master into offsetCurve

Conflicts:
	h2spatial-ext/src/test/java/org/h2gis/h2spatialext/SpatialFunctionTest.java

Add javadoc for ST_LineIntersector and ST_OffsetCurve functions
Improve unit tests
Merge irstv/master into offsetCurve

Conflicts:
	h2spatial-ext/src/test/java/org/h2gis/h2spatialext/SpatialFunctionTest.java

Add javadoc for ST_LineIntersector and ST_OffsetCurve functions
Improve unit tests
Merge pull request #420 from ebocher/offsetCurve

Offset curve
New function ST_OffsetCurve to compute an offset line or collection of lines at a given distance and side from an input geometry.