Complete filter examples

Address #86

Filter example includes comparison between a filter and the MKS. The
example has been simplified with added explanation and the notation is
consistent with other examples. Further work is needed to show how the
modified coefficients reproduce the filter.
Add filter example to the web page

Address #86

Fix some typos in filter.ipynb as well.
Merge branch 'master' into issue86-filter
Merge pull request #96 from wd15/issue86-filter

Issue86 filter