v0.4.0 - Githubissues

Describe your changes

Add better support for multi-panel graphs via mpanel_e61() (referring to combining multiple discrete graphs into a single panel, not faceted graphs).
Add dual y-axis support allowing for graphs with secondary y-axes with different scales to be created.
Add experimental automatic graph height calculation in save_e61(), which should reduce the need for users to manually specify height when saving graphs.
Correct whitespace margins around graphs.
Improvements to various documentation.

[x] I have written tests covering functions I have added or changed.
[x] I have run tests and they all pass.
[x] I have ensured all new functions will show up in the _pkgdown.yml file.
[x] I have updated DESCRIPTION with any new package dependencies.
[x] I have updated NEWS.md with a brief description of my changes.
[x] I have updated the package documentation with devtools::document().
[x] I have updated the package website with pkgdown::build_site_github_pages().