Attempt to avoid potential CRAN issues if IEEE API is down

If the IEEE API is down, tests at CRAN (once we put the package there) would give errors. Attempting to avoid this.

- Add a function to test for connection to IEEE
- If no connection, skip the rest of the tests
- Add \donttest{} to all examples
- If no connection in building vignette, abort early
- Include pre-built vignette and add `BuildVignettes: no` to `DESCRIPTION` file.
- `R CMD check` will still give an error when running vignette code, but it should be more clear.