Fixes for Nortek Altimeter Measurements

[jmcvey3]

PR to resolve:

1. Reader bugs discovered in Issue #122
2. Corrections to altimeter variable names and metadata based on Nortek software data output
3. Add AWAC altimeter measurements to reader

TODO

• [x] Verify that bugs are resolved
• [x] Verify and update tests

[coveralls]

Pull Request Test Coverage Report for Build 7188198204

• 45 of 95 (47.37%) changed or added relevant lines in 9 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.7%) to 88.636%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
dolfyn/tests/test_read_adp.py	7	8	87.5%
dolfyn/io/nortek2.py	13	15	86.67%
dolfyn/io/nortek.py	2	49	4.08%
<!--	Total:	45	95	47.37%	-->

Files with Coverage Reduction	New Missed Lines	%
dolfyn/io/nortek2_defs.py	1	95.95%
dolfyn/tests/test_read_adp.py	1	80.29%
<!--	Total:	2		-->

Totals
Change from base Build 7185583123:	-0.7%
Covered Lines:	5413
Relevant Lines:	6107

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💛 - Coveralls

[jmcvey3]

@lkilcher Would like to merge PR #124 first, then this one. The reason for recreating all the Nortek ad2cp test files was because I changed the ID tag names in the "burst_config" attribute.