Merge branch 'transitions-span-link' into issue-833

src/changes/changes.xml

src/main/java/org/orekit/attitudes/AttitudesSequence.java

src/main/java/org/orekit/files/sinex/SinexLoader.java

src/main/java/org/orekit/files/sinex/Station.java

src/main/java/org/orekit/forces/drag/TimeSpanDragForce.java

...ekit/forces/empirical/TimeSpanParametricAcceleration.java

src/main/java/org/orekit/gnss/antenna/AntexLoader.java

src/main/java/org/orekit/gnss/clock/RinexClock.java

...earth/troposphere/TimeSpanEstimatedTroposphericModel.java

src/main/java/org/orekit/utils/TimeSpanMap.java

src/test/java/org/orekit/gnss/ClockFileParserTest.java

src/test/java/org/orekit/utils/TimeSpanMapTest.java