Fix IQR Inclusion

Looking at the example provided by @pascalmartin (Issue #5), it looks like the calculated IQR is 0 because the 25th and 75th percentile are the same (22.5). Going from `iqr()` to the following `band_pass()` I think is where the perceived trouble arises.

This commit and test shows a "fix" if you desire to have the IQR filter include the values. This depends on intended behavior. (Feel free to deny it if it goes against intended IQR behavior.)