Using Environmental Variable to set a flag to an empty string

[johnlockwood-wf]

One of the caveats of using an env var to override what is set in the ini is that it is ignored if you want to make the flag an empty string. I am trying to come up with a way to make this possible.
I think an enhancement to globalconf is the place it should be instead of requiring the programmer to come up with some non-empty-string that means empty-string.
Perhaps have a pattern like EMPTY_ENVPREFIX_FLAG_NAME=true. What do you think?
I'd be happy to make a PR.

[rakyll]

os.LookupEnv allows us to see if the env var actually exists. We should facilitate this function rather than using os.Getenv.

Wouldn't it solve the case you are mentioning?

[johnlockwood-wf]

Yes. I'll try my hand at making a PR for it.