Generate html manuals in extractManuals

[jwokaty]

May alternatively fulfill creating html manuals mentioned in #15. Creates html manual in the same function as the pdf manual and places it in the pkg/man/pkg.html path.

Note: This doesn't seem to be the way that manuals are created anymore although there's some cruft in the BBS code pointing to it. Keeping for referencing temporarily.

[LiNk-NY]

Hi Andres, @jwokaty

I reviewed the code and the proposed change.
The code written here only works for data/annotation packages which should come shipped with PDF manuals (as we don't build them with the BBS).
Perhaps Lori @lshep can provide more context but the current proposed changes in this PR would only affect annotation packages and not all the software packages as intended.

[jwokaty]

@LiNk-NY Thanks for looking at this. I realized that it doesn't work for all packages and it may not be used by the BBS anymore. Software manuals (data experiment and maybe some annotations too) are pulled from R.check folders, which is done during the BBS postrun so I am making changes there Bioconductor/BBS#438. I put this in WIP until I can assess if this is still being used. Maybe it's only used for the packages that aren't built by the BBS?