Remove tidymodels dependency + Silence R CMD CHECK warnings

[olivroy]

• Delete the docs/ directory (gh-pages branch allows to follow changes made to the website) + add to .gitignore
• Use testthat setting (without loading libraries)
• More namespace
• Remove unneeded library(timetk) in examples.
• Remove dep on tidymodels, and yardstick.
• Use dev version.
• T -> TRUE, F -> FALSE
• Use tidyselect::all_of() when specifying an external vector.
• Silence timezone warnings in tests by adding a temporary expect_tz_warning() function before Warnings in tests #156 is fixed.

This reduces the number of dependencies to 127 (down from 148 at first),

[olivroy]

@mdancho84 , all CI pass now, let me know what you think!

[mdancho84]

Looks good. I'll check on my end after the merge.

One thing: there is a FANG data set with timetk. Please leave that one as is.

Just in case someone needs the old version I can have them use timetk FANG.