Implement Atmosphere Model

[rdoddanavar]

Implement U.S. Standard Atmosphere 1976

[rdoddanavar]

Consider creating follow-on issue to add other models:

• ISA
• CIRA-86
• COESA
• NRLMSISE-00
• JB2008
• etc.

Useful links:

• https://space.stackexchange.com/questions/34631/is-the-standard-model-of-atmosphere-the-same-as-nrlmsise-00

[rdoddanavar]

Resources for humidity/density interaction:

• https://www.google.com/url?sa=t&source=web&rct=j&url=https://commons.erau.edu/cgi/viewcontent.cgi%3Farticle%3D1124%26context%3Dijaaa&ved=2ahUKEwiAu-ztn830AhVFOs0KHVCuCcM4FBAWegQIBRAB&usg=AOvVaw1pMy02CmT8uPbfku2tZ6uC
• http://www.wind101.net/air-density/air-density-calculator.htm