Merge pull request #2 from alchemyst/master

Updating repo
Sage versions of textbook examples

Two examples from the textbook, as well as some interactive tools built
some time ago to better understand transfer functions and their
relationship to the time domain
Merge pull request #78 from bsaaiman/master

Example 2.2, allowable delta's from page 262, two interactive transfer function examples
Merge pull request #79 from Fugacity59/master

Solved Example 7.7