R CMD CHECK fails when building vignette

There are no errors when checking the package proper. But when it gets to the Vignette it generates this error:
```
Error: package or namespace load failed for 'tbltools' in loadNamespace(j <- i[[1L]], c(lib.loc, .libPaths()), versionCheck = vI[[j]]):
there is no package called 'data.table'
Quitting from lines 13-18 (fmatch_performance.Rmd)
Error: processing vignette 'fmatch_performance.Rmd' failed with diagnostics:
package 'tbltools' could not be loaded
--- failed re-building ‘fmatch_performance.Rmd’

SUMMARY: processing the following file failed:
‘fmatch_performance.Rmd’

Error: Vignette re-building failed.
Execution halted
```

Note that `tbltools` is on the server. It is not explictly mentioned in `Suggests:`, but I believe it is imported by other packages which the package mentions in the DESCRIPTION file. So it is not exactly clear why the package cannot be found.

One possible theory is that R CMD CHECK might be doing some kind of strict verification to make sure that each package can be installed. Note, however, that the tbltools repository is private on github: https://github.com/BAAQMD/tbltools. So tbltools might not be able to be "found" under that criteria.

Another theory is that fmatch and tbltools both import/suggest/depend on each other, which might be causing a problem.

Start by reproducing R CMD CHECK and inspect DESCRIPTION alongside fmatch_performance.Rmd, especially lines 13-18, to trace the missing data.table dependency. Review the reported tbltools relationship and dependency declarations. Done when the vignette rebuilds without the package-load error and R CMD CHECK passes.

Written by the indexing model from the issue text.