update exmaples, fix site file extension check

etc/examples/1-hazard-curve/README.md

etc/examples/1-hazard-curve/site.csv

etc/examples/2-custom-config/README.md

etc/examples/2-custom-config/site.csv

etc/examples/3-sites-file/README.md

etc/examples/4-hazard-map/README.md

etc/examples/5-complex-model/README.md

etc/examples/5-complex-model/config-sites.json

etc/examples/6-enhanced-output/README.md

etc/examples/6-enhanced-output/config.json

etc/examples/7-deaggregation/README.md

etc/examples/7-deaggregation/config.json

etc/examples/8-probabilities/README.md

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