removal of master/slave from source code

[Mike Fulton]

Hi,

I would like to propose changing the terminology in the vim code from 'master/slave' to a more inclusive, and hopefully more accurate, set of terminology.

Most occurrences are in the 'pty' code.

I am happy to work with folks on what the proper replacement terms could be - perhaps 'controller' and 'controlled' ?

Thanks, Mike Fulton