Make Guide and API Docs print-friendly

[sorcamarian]

Currently, this is how these sections(Guide and API Docs) appear in Chrome(v52) print-mode(ctrl + p):

I suggest the use of CSS ``@media print` rule in order to:

• hide the navigation and sidebar sections
• remove the left margin from the content section

In code:

@media print {
  .sidebar,
  .nav { 
    display: none; 
  }
  .content {
    margin: 0;
  }
}

After the CSS codes were added:

Commit NOTE:
Because LESS is used, I have split the codes and added them in the appropriate files.

[abernix]

@sorcamarian Could you open a PR for this? It appears you made the commit on your own branch but never opened the actual PR. 😉