Update documentation to be coherent with the style guide

[tin1254]

• update include guard to #pragma once
• fix broken link to the style guide

The include guard bilateral.hpp is still in the old style, I will update it when I refactor other filters later

[kunaltyagi]

Might have to see visually to verify, but that's after merge

[jmaiolini]

I think we could use this PR to update also the LICENSE blurb to use the new one when writing a class. What do you think @kunaltyagi ?

[kunaltyagi]

Blurb in this rst file? Sure. But not in actual code files

[jmaiolini]

Yes, speaking about the doc, not actual code!

[tin1254]

This one? Maybe we should also add this to the style guide in a new PR

[kunaltyagi]

Would it be considered a style guide? Isn't that more for code? We do have a blurb in contributing.md for reference

[tin1254]

Personally I would consider it as style guide (Google Style Guide also include in their guide)

But maybe updating this file is enough for new contributors, as anyone wanted to implement a new class will definitely look at this rst

[tin1254]

also I found the links to the class are also broken (e.g. `:pcl:pcl::Filter<pcl::Filter>` in the page), we may want to update the doxylink here from http://docs.pointclouds.org/trunk/ to https://pointclouds.org/documentation/

but I'm not sure if it's correct as I didn't use doxylink before

[kunaltyagi]

Paging @larshg for assist in doxylink

[kunaltyagi]

This changeset looks self-contained. Please use other PRs for doxylink corrections or other improvements :)

[mvieth]

Nice!

[larshg]

Paging @larshg for assist in doxylink

I'm not familiar with doxylink or the like, sorry.