Ignore all arguments when starting server and use envvars instead. Read NANO_POW_EFFO...

Ignore all arguments when starting server and use envvars instead. Read NANO_POW_EFFORT from environment when starting server. Update test script to use port 3001 to test custom value. Pass NanoPowOptions object into puppeteer evaluate calls. Update README to use destructuring assignment for output clarity and to use new method names. Add more command line guidance to README. Fix default effort used by server to match the actual implementation and fix README accordingly. Add --server documentation to manual. Fix threshold/difficulty ranges throughout documentation and remove mention of u32 threshold workaround from README. Whitespace.