Add mercurial script

[pele1410]

I added support for tracking mercurial repositories similar to the existing git repository support.

set -g @dracula-plugins "hg time"

Clean repository

Dirty repository

Tested each configuration:

set -g @dracula-hg-disable-status true
set -g @dracula-hg-show-diff-symbol "^"

set -g @dracula-hg-no-untracked-files true

set -g @dracula-hg-no-repo-message "no-hg"

set -g @dracula-hg-show-current-symbol "@"

[ethancedwards8]

Thank you for your contribution!