replaced all instances of master with main

[barronkid]

Trying to facilitate some thoughtful change surrounding the words we use. This fork blindly replaced all uses of the word 'master' (based on its natural relation to the word 'slave') allowing us to easily adopt the alternative term 'main'.

Submitting back to you here for your consideration as an 'improvement', or the beginning of a new permanent fork or branch could prompt/encourage the user to migrate to the use of 'main'.

[ChrisJStone]

Could you please kindly resubmit your pull request against my fork of gitflow here. I have no issues with the proposed changes you suggest. Though since the newer versions of git allow us to define a default branch name perhaps we might be able to find a better word that does not imply we have to use "main" as the default branch.