prob and rate to maths; mfds tests

src/main/java/gov/usgs/earthquake/nshmp/Maths.java

src/main/java/gov/usgs/earthquake/nshmp/calc/EqRate.java

...ain/java/gov/usgs/earthquake/nshmp/calc/HazardExport.java

...ain/java/gov/usgs/earthquake/nshmp/calc/ReturnPeriod.java

src/main/java/gov/usgs/earthquake/nshmp/data/Sequences.java

src/main/java/gov/usgs/earthquake/nshmp/mfd/Mfd.java

src/main/java/gov/usgs/earthquake/nshmp/mfd/Mfds.java

...java/gov/usgs/earthquake/nshmp/model/FaultRuptureSet.java

src/test/java/gov/usgs/earthquake/nshmp/mfd/MfdsTests.java

...t/java/gov/usgs/earthquake/nshmp/model/peer/PeerTest.java