Added missing function's documentations

[wverastegui]

This PR added the documentation of the following functions:

• compute_densities
• compute_mass_values
• compute_mz_sd
• draw_rt_correction_plot
• draw_rt_normal_peaks
• extract_pattern_colnames
• get_num_workers
• increment_counter
• plot_normix_bic
• plot_peak_summary
• plot_raw_profile_histogram
• plot_rt_profile
• span

Closes https://github.com/RECETOX/recetox-aplcms/issues/150

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 66.42%. Comparing base (6ac2542) to head (50ffc18). Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #225 +/- ## ======================================= Coverage 66.42% 66.42% ======================================= Files 23 23 Lines 2740 2740 ======================================= Hits 1820 1820 Misses 920 920 ```

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