Support pijul

[yoichi]

Add support for pijul (https://pijul.org/) and its repository hosting service the Nest (https://nest.pijul.com/)

% ghq get -u https://nest.pijul.com/pijul/nest
     clone https://nest.pijul.com/pijul/nest -> /Users/yoichi/ghq/nest.pijul.com/pijul/nest
     pijul clone https://nest.pijul.com/pijul/nest /Users/yoichi/ghq/nest.pijul.com/pijul/nest
Repository created at /Users/yoichi/ghq/nest.pijul.com/pijul/nest
Downloading changes [==================================================] 1/1
           Applying [==================================================] 1/1
 Completing changes [==================================================] 0/0
% ghq get -u https://nest.pijul.com/pijul/nest
    update /Users/yoichi/ghq/nest.pijul.com/pijul/nest
     pijul pull
Downloading changes [==================================================] 0/0
Nothing to pull

[Songmu]

This is a feature we wanted. Thank you! Released as v1.5.0.

ref #319