Create first functions to import data and visualise result

[LukasWallrich]

Create functions to

• [x] import data and specify key variables
• [x] run fixed-effect and random-effect meta-analyses
• [x] show forest plot and funnel plot

Write examples / unit tests for 2-3 psymetadata tests

• [x] Barroso2020
• [ ] Aksayli2019
• [ ] Coles2019

[LukasWallrich]

Closed - have used a different dataset for ESMARConf tutorial and would rather use that than just more.