Add new study: Purdie_1976

[yangsophieee]

A study examining vegetation regeneration after burning in dry sclerophyll communities near Canberra. Data were transcribed from original manuscript.

Need to check taxonomic updates for this study still, @ehwenk.

A few questions for review:

• Not sure about their affiliation, I think they are long retired
• Unsure whether the location property 'temperature, monthly max (C)' corresponds to the average of all mean monthly maximum temperatures
• Please double check my mapping of site information to geology (parent material) and geology (stratigraphic map unit)

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (eb020c6) 80.20% compared to head (1bb20c6) 80.20%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #698 +/- ## ======================================== Coverage 80.20% 80.20% ======================================== Files 7 7 Lines 1531 1531 ======================================== Hits 1228 1228 Misses 303 303 ```

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