Plutobio

Minor improvements

* Simplified API request syntax for increased performance and improved maintainability

Major changes

* Added family of `pluto_get_*()` functions to retrieve data from the Pluto API

* Added family of `pluto_read_*()` functions to read Pluto data directly into a data.frame

* Added function `pluto_add_experiment_plot()` to upload HTML and image files to an Experiment in Pluto