Enable test_read_2_sample_minimal to pass

[dcslagel]

@JustinGOSSES,

This change enables the test-sample_2.0_minimal to pass.

Here are the main changes:

• las2json tests are moved to standalone test files in dist/test/las2json/text*.js. This is so we can run a single test via 'tape dist/test/las2json/[test-name]. They can be run as a group with npm run test-las2json
• The main split on the tilde section indicator is changed to include the tilde in the string. This is done so that the sections can be identified with tilde and initial letter.
• The parser that skipped the first 3 lines of some sections is changed to just skip the first line (the section title line). Then only if the subsequent lines are comments (starting with '#') they are skipped in the 'if' check. This is done because the sample_2.0_minimal.las file doesn't have the 2 comment lines that follow the section title.
• If Curve headers are not found in the ~A title line, code has been added to try and get the headers from the Curve Information Block keys, and if that fails then it create a set of default headers of 'COL[incremented number] (example: COL1, COL2, ...)'.

Let me know if this change could be accepted (or rejected) or needs some additional changes before merging.

Thanks,

DC

[JustinGOSSES]

Looks good.