Add more tests for utils

[laanwj]

• Add tests for html_parsing, proxycheck, random, remove_duplicates, url_parsing (everything that doesn't require networking)
• Add a check to GenerateRandomBytes for negative values.

Increases coverage:

ok      github.com/s-rah/onionscan/utils        0.009s  coverage: 30.5% of statements
ok      github.com/s-rah/onionscan/utils        0.035s  coverage: 72.6% of statements

[coveralls]

Coverage increased (+4.8%) to 31.103% when pulling 7608dca on laanwj:2016_11_util_tests into 751cc8a on s-rah:onionscan-0.3.

[s-rah]

Awesome! Thanks!