Don't load lubridate on startup + other upkeep

[olivroy]

This should fix #116 , supersedes #163 (I think it's better to rely on cli's inline theme, rather than RStudio, as it makes the package more portable.

Using how tidyverse loads its packages rather than base R to create less clutter when loading the package.

Removing packages from depends

You will note that I tweaked the vignettes loading scheme.

Showing library(tidyverse), library(tidyquant)

actually running library(dplyr) library(lubridate) etc. library(tidyquant)

I also added skip() to avoid test failures when APIs are not available.

Move tq_performance() and tq_transmute() lists of functions into an internal data, as I assume that xts, quantmod are quite stable and if there are any new functions, it is always possible to re-run the data-raw script and update the possible functions.

Addresses #235

Edit: closes #91

[olivroy]

I also changed xlim and ylim so that the example doesn't show as blank.
https://business-science.github.io/tidyquant/reference/geom_ma.html

Do you know why the 75-125 lims are not correct anymore?

eb5099a#diff-c53cfe3cb0db9e7cb411222ea0b11a7dd25ed649bd6e7ad9bce1b66f73abe0fc
they seemed correct here?

[olivroy]

@mdancho84 let me know if you think these changes are too agressive!

But I think there is an added value here as there are less messages on startup, and the new startup messages are more familiar for tidyversee users)

[mdancho84]

Looks good to me. I felt it was an improvement and simplification. Plus fewer dependencies too.

[mdancho84]

Let me know if you want to help out on some other things. Shoot me an email at [email protected]