Added specs for different schemes in editor URLs
Added BetterErrors.default_editor method to sniff EDITOR

Provides an optional facilitator method for sniffing a complaint
BetterErrors.editor symbol based on the EDITOR env var.
Defaulted BetterErrors.editor based on EDITOR automatically

Makes a smart, automatic assumption of what you'd like the default URL
scheme to be for files based on the EDITOR environment variable.
Merge pull request #188 from rmm5t/default-editor

Provide an automatic, smart default for BetterErrors.editor