Fix package overview help file

Dear maintainer,

You have file 'RprobitB/man/RprobitB.Rd' with \docType{package}, likely
intended as a package overview help file, but without the appropriate
PKGNAME-package \alias as per "Documenting packages" in R-exts.

This seems to be the consequence of the breaking change

  Using @docType package no longer automatically adds a -package alias.
  Instead document _PACKAGE to get all the defaults for package
  documentation.

in roxygen2 7.0.0 (2019-11-12) having gone unnoticed, see
[<https://github.com/r-lib/roxygen2/issues/1491>](https://github.com/r-lib/roxygen2/issues/1491).

As explained in the issue, to get the desired PKGNAME-package \alias
back, you should either change to the new approach and document the new
special sentinel

  "_PACKAGE"

or manually add

  @aliases fHMM-package

if remaining with the old approach.

Please fix in your master sources as appropriate, and submit a fixed
version of your package within the next few months.

Best,
-k
loelschlaeger / fHMM

Fix package overview help file #90
