Fix plot weather data func

[chenzhao2020]

Addressed various fixes from Marco and Chad's reviews:

• Marco:

  • Simplified the repeated codes in plot_weather_data() function
  • Set default parameters for time_basis and col_name argument of plot_weather_data() function
  • Fix single quote mark problem in plot_weather_data() function's docstring
  • Add explaination of how to get the obs_df in plot_weather_data() function's docstring

• Chad:

  • Delete tests/test_noaastn.py file
  • Written plot_weather_data() function in a more DRY fashion based on the suggestion, thank you for that!
  • Labled x-axis nicely when using the plot_weather_data() function with "daily"argument

[codecov]

Codecov Report

Merging #48 (5b6e33a) into main (df91c5e) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #48   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines          176       165   -11     
=========================================
- Hits           176       165   -11     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
noaastn/__init__.py	100.00% <100.00%> (ø)
noaastn/noaastn.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2db5d4b...5b6e33a. Read the comment docs.