Allow processing stdin, file descriptors

[buglloc]

Must resolve #32
Now Gixy can read configuration file form stdin (use - as a file path):

$ nginx -T | gixy  -
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
[nginx_parser]	INFO	Switched to parse nginx configuration dump.

==================== Results ===================
No issues found.

==================== Summary ===================
Total issues:
    Unspecified: 0
    Low: 0
    Medium: 0
    High: 0

Or file descriptor:

$ gixy <(nginx -T)
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
[nginx_parser]	INFO	Switched to parse nginx configuration dump.

==================== Results ===================
No issues found.

==================== Summary ===================
Total issues:
    Unspecified: 0
    Low: 0
    Medium: 0
    High: 0