change to cran style and add page site

[lidanwu]

This PR cleans up the style of the following documents for cran package submission and adds a github pages site for manual.

• call out @importFrom for functions from stats, methods, utils, all of which are part of Part of R 3.6.2 and shared the same GPL-2 | GPL-3 license.
• call out @importFrom data.table ':=' .N .SD
• include URLs and additional repositories links to DESCRIPTION for bug reports and package in suggests.
• fix @examples of some functions to make sure each row does not have more than 100 characters; this way the pdf generation of manual looks good.
• add github workflow for automatic generation of github pages site; the local rendering of the site looks ok.

This PR has passed

• unit tests,

• devtools::build_man() with corrected formatted pdf manual

• R CMD build which generates the vignettes,

• R CMD check from tarball.

For proper publishing the page site,

• [ ] this PR needs to merge into master branch
• [x] deploy the local articles and built site to gh-page branch. This would require configure the github workflow to install all R dependencies properly.
• [ ] configure in repository settings to publish the repository and the page site

[lidanwu]

I managed to deploy a pre-built version of pages site at gh-pages branch and now it's live at https://nanostring-biostats.github.io/FastReseg/ . While automatic github action workflow is still desired to automatically rebuilt the site upon PR, the static version should be good for quite some time.