Handle duplicate headers and changing number of data columns.

[dcslagel]

Description:

Handle duplicate headers and changing number of data columns. This pull-request enables parsing some of the LAS files in issue:

• more malformed LAS files from USGS to handle, mostly florida #61

Changes to dist/index.js:

• Only read a required unique header and its data once. Ignore additional entries for the unique header. These are the headers: ~V, ~W, ~C, ~P, ~O, and ~A.
• Move the inital parsing from las string data in interim structured section data to sub-function: las2json.readSections()
• Move las2json sub-functions to the bottom of the section to make the main logic more prominent.
  • Handle cases of data sections that have an inconsistent number of data columns in the data rows. If a row has more data columns than the headings, then add generic colunms titled 'UNKNOWN' + a number. Then populate the previous rows for that column with zero string values '0'

Add tests:

• dist/test/las2json/test_duplicate_header.js
• dist/test/las2json/test_extra_data_columns.js

This is a fairly big change, with moving some code sections around and replacing some code with a sub-function.

Test Results:

npm run test-las2json
...
1..50
# tests 50
# pass  50

--

Let me know if this change could be accepted (or rejected) or needs some additional changes to be approved and merged.

Thank you, DC

[JustinGOSSES]

Sorry I've been slow on this one. Will try to review this within the week. As you say, it's a bigger change than normal, so want to give it a good review.