Clear methodology for masculine and feminine forms of words

[jmccrae]

This pull request fixes #883

I decided not to introduce an explicit relationship for masculine/feminine as there was not a clear way to proceed with this. This is due to there being several cases:

1. A masculine term and a feminine term with a clear gender-neutral term ('policeman'/'policewoman'/'policeperson')
2. A feminine term and a gender-neutral term ('actress'/'actor')
3. Some terms where a gender-neutral synset does not exist or would be artificial (e.g. 'viscountess')

Instead, this change aims to ensure that no synset contains both a masculine and a feminine form, and wherever the forms are specifically gendered the synset is a hyponym of man 10306910-n or woman 10807146-n