add troposphere coefficient offsets

[semuadmin]

pyspartn Pull Request Template

Description

1. Fixed offsets added to troposphere attributes, in accordance with SPARTN 2.0.2 specification:

   • SF043 (Area average vertical hydrostatic delay )-> add 2.3m
   • SF045 (Small troposphere coefficient T00) -> add 0.252m
   • SF048 (Large troposphere coefficient T00) -> add 0.252m

   Thanks for @jonathanmuller for contribution.

Fixes #30

Testing

Please test all changes, however trivial, against the supplied pytest suite tests/test_*.py. Please describe any test cases you have amended or added to this suite to maintain >= 90% code coverage.

Checklist:

• [x] I agree to abide by the code of conduct (see CODE_OF_CONDUCT.md).
• [x] My code follows the style guidelines of this project (see CONTRIBUTING.MD).
• [x] I have performed a self-review of my own code.
• [x] (if appropriate) I have cited my public domain SPARTN documentation source(s).
• [x] I have commented my code, particularly in hard-to-understand areas.
• [x] I have made corresponding changes to the documentation.
• [x] (if appropriate) I have added test cases to the tests/test_*.py pytest suite to maintain >= 90% code coverage.
• [x] I have tested my code against the full tests/test_*.py unittest suite.
• [x] My changes generate no new warnings.
• [x] Any dependent changes have been merged and published in downstream modules.
• [x] I have signed my commits.
• [x] I understand and acknowledge that the code will be published under a BSD 3-Clause license.