Physiology vignette

[dfalster]

Currently builds from tree, so waiting on #2

Check if want to keep existing content or copy over from growth_trajectories. Tables there probably also useful

[dfalster]

• [x] Table of variables
• [x] Mortality model
• [x] Fecundity
• [x] Schematic
• [x] leaf photosynthesis
• [x] trait effects
• [x] reproductive allocation
• [x] germination probability