niceday version 1.0.0

[svteichman]

• updates version to 1.0.0 (addressing issue wishlist: package version #4)
• fully documents two exported functions (ndFit() and est_nuis())
• adds print function for ndFit output
• updates inputs to ndFit() so that A and X are formulas and a data argument is included (addressing issue wishlist: IO #3)
• if X is not included or is the intercept model returns Psi1 and Psi1g estimates, otherwise returns Psi2 and Psi2g
• updates structure of outputs and names of output components
• adds and documents data
• includes preliminary version of intro vignette

[svteichman]

@gthopkins things that this PR could use from you (either edits to this PR or a separate PR after merging this one):

• add additional testing for features you think are relevant in "tests/testthat/test-ndFit.R"
• somewhere (either in ndFit documentation, the README, or the vignette) give your recommendations on the list of learners that you would suggest for each of sl.lib.pi, sl.lib.m, sl.lib.q
• review the README and vignette and make/suggest changes (you and @adw96 can decide which of you should review these/in what order so you don't overwrite changes)

@adw96 things this PR could use from you:

• refinement of README brief description
• refinement of vignette (I ended up writing a draft that discussed the assumptions and related parameters because I wasn't sure how much we wanted to include, but feel free to remove if you think it'll be distracting to users - and of course to make any other changes!)

[adw96]

@svteichman having made my edits as you suggested, I'm going to merge this, and @gthopkins can add more tests / vignettes/ any other input at any time.

Thank you for the AMAZING vignette -- it was even better than I expected, and I SO appreciate you doing it. ❤️❤️❤️ I'm very grateful...