Disqus and other enhancements

* Disqus support: Just edit the variables global_disqus and global_disqus_username to enable comments. Needs a Disqus account.

* (Optionally) Reads configuration from an external file. I made this so it's easier to merge code from others without rewriting options in bb.sh. You can also mantain different blogs in the same machine. Copy the  configuration variables to ".config" or set another path for the file.

* It detects if you're using a BSD version of date, and tries to use gdate in that case.

* Changed 
```date -r $1 +'%Y%m%d%k%M' ``` to 
```date -r $1 +'%Y%m%d%H%M' ```. 
It produced an output with spaces when hours where under 10 and later touch complained about wrong timestamps.