implementation of Spudich et al. (1999) for PRVI 2003

src/main/java/gov/usgs/earthquake/nshmp/gmm/Gmm.java

.../gov/usgs/earthquake/nshmp/gmm/SpudichEtAl_1999_PRVI.java

src/main/resources/gmm/coeffs/SEA99-PRVI.csv

src/test/java/gov/usgs/earthquake/nshmp/gmm/SEA99_test.java

src/test/resources/gmm/sea99-inputs.csv

src/test/resources/gmm/sea99-results.csv