Get rid of warnings and notes from rcmdcheck

[Bai-Li-NOAA]

This pull request resolves issue #48 by implementing the following changes to eliminate warnings and notes that appear during the execution of devtools::check():

• Replace the use of tools:::RdTags with lapply() to retrieve tag names in R/validate_Rd.R.
• Update roxygen documentation and use importFrom to import functions from external packages
• Update the LICENSE file through the {usethis} package and included it in the DESCRIPTION file.
• Restructure the project's file organization by relocating all R scripts from the root directory to the inst/ subdirectory.

[kellijohnson-NOAA]

@Bai-Li-NOAA thank you so much for fixing these things. If you don't mind, I would like to force push a change to this branch that will better align with the other changes that we have made in synonym where we use :: rather than importFrom. I like the former better than the latter because it gives other readers a better chance at knowing where the function comes from because you technically do not have to import a function from another package more than once, which can lead to the importFrom not being in the .Rd for every relevant function, which can be confusing.

[Bai-Li-NOAA]

@kellijohnson-NOAA , great. please feel free to force make any changes to this branch!