Pre-release fixes

[pratikunterwegs]

This PR makes pre-release fixes:

1. Updates to functions to allow counts rather than strict integers, with distinctions between functions in whether 0s are allowed or not,
2. Updates to function documentation with links to parameter sources,
3. Updates to README to add install instructions, fix urls, and correct workflow,
4. Guard tests against noSuggests runs on CRAN; this issue still affects the vignettes so the addition is moot,
5. Adds NEWS and CRAN comments files

Changes from code review in #103

1. Fixes Single convolution function for cases and PMFs #106 by adding the function .convolve_cases_pmfs(),
2. Fixes Test for bias due to index shifting #108 by adding tests for cfr_time_varying()

[pratikunterwegs]

Snapshots tests for ascertainment failing as ascertainment is much higher; this is noted and being looked into.

[github-actions]

This pull request:

• Adds 0 new dependencies (direct and indirect)
• Adds 0 new system dependencies
• Removes 1 existing dependencies (direct and indirect)
• Removes 1 existing system dependencies

(cc @Bisaloo for workflow monitoring)

[pratikunterwegs]

Deleting comments from the GH dependencies action bot. One comment retained for information re: {outbreaks} pkg removed.