specify the `filters` argument in the `addPackage()` function as well as in the `makeRepo()` function.

[indenkun]

Dear Developers and Maintainers.

The makeRepo() function was fixed in Issue #156 to pass the filters argument to pkgAvail(), but the addPackage() function, which uses the makeRepo() function internally, still cannot specify the filters argument to be passed to the final pkgAvail() function, so that default value filters = NULL is set, and the same problem as in #156 is occurring in the addPackage() function.

As in #156, this can be solved by setting available_packages_filters, but if the addPackage() function can specify the filters argument and pass it to the makeRepo() function, everything can be solved in the function, This would be more preferable.

I would appreciate it if you could consider this.