Add External Resources section to specification

[esilvia]

It might be helpful to add a section linking some official external resources. Some ideas off the top of my head:

1. Official LAS GitHub wiki (https://github.com/ASPRSorg/LAS/wiki)
2. USGS LBS (implementation example, reference specification: https://pubs.er.usgs.gov/publication/tm11B4)
3. 2014 ASPRS Accuracy Standards (http://www.asprs.org/a/society/committees/standards/Positional_Accuracy_Standards.pdf)
4. Lewis's LAS 1.4 PE&RS article from February 2012

I'm not sure whether it makes more sense to include as a part of the intro (§1) or maybe at the end, in a section that includes the LDPs (§6). Alternatively, since providing external links creates the possibility of dead links in a static specification, maybe this should instead be a link to an External Resources wiki page.

[csevcik01]

A link to an external resources page seems useful to me. But it has to be clear that such additional ressources is of explanatory nature and not part of the standard.
To avoid dead links, I would refrain from direct linking, but refer to a single resource page instead.
The LAS Wiki page might be a candidate?

[esilvia]

Added the External Resources wiki page today like @csevcik01 suggested: https://github.com/ASPRSorg/LAS/wiki/External-Resources

I ended up not including links to news outlets.

[esilvia]

I added section 1.4 in this draft PDF:

LAS_issue_71.pdf

I don't really like the title of that section... should I just call it "Other Resources"?