remove dplyr and tibble from dependencies

[EvgenyPetrovsky]

this PR resolves #1

tidy verse takes ages to install and check in travis. it is also very heavy when being installed on workstation. this change removes dependency on dplyr: mutate function and arrange function. These two functions were replaced with core R functionality but with help of magrittr package to make it less imperative and more compositional:

• Function dplyr::mutate was replaces with inset (df[x] <- ... is the same as df %>% inset("x", value = ...))
• Function dplyr::arrange was replaced with extract (df[order(x),] is the same as df %>% extract(order(.$x),))

[codecov-io]

Codecov Report

Merging #6 into master will increase coverage by 0.92%. The diff coverage is 0%.

@@            Coverage Diff             @@
##           master       #6      +/-   ##
==========================================
+ Coverage      16%   16.92%   +0.92%     
==========================================
  Files           2        2              
  Lines         125      130       +5     
==========================================
+ Hits           20       22       +2     
- Misses        105      108       +3

Impacted Files	Coverage Δ
R/utils.R	0% <0%> (ø)	:arrow_up:
R/generator.R	29.72% <0%> (+2.7%)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 7c05771...1f15f12. Read the comment docs.