These things are picked up if they are installed, and as they are pretty
lightweight we may as well mark them as optional deps.
Signed-off-by: Jack Nagel <jacknagel@gmail.com>
Given the API incompatibilities between 1.x an 2.x, it is easier to
maintain separate formulae for the time being. Luckily, the developers
have made sure that the two can be installed alongside each other: the
binaries have different names, the library is versioned, &c.
ClosesHomebrew/homebrew#7345.
Signed-off-by: Jack Nagel <jacknagel@gmail.com>