Add video link to evaluateGeometricSeriesFraction

Add link to video for the second question of the Week 2 Homework.
fixes #016
Still would like to rewrite part of the ratio test proof
Draft of textbook for week 3
Fix typo: smaller -> small.
Fix typo: ...is [to] think....
Reflow nth term test warning.

This is a perhaps more readable alternative than the hanging side note
after the warning block.
Fixed typo: because -> being.
Fixed a couple of example/solution typos.
Fixed type: we shown -> we've shown.
Merge pull request #17 from mateor/master1

Add video link to evaluateGeometricSeriesFraction
Merge pull request #19 from clark-archer/series-2.5

Fixed a couple of typos in section 2.5.
Merge pull request #21 from clark-archer/series-2.7

Fixed some typos in section 2.7.
Merge branch 'master' of github.com:kisonecat/sequences-and-series
Cleaned sidenote
Integral test now stated for series with initial index k
Fixed initial index in value of series
Update root-test.tex

Minor typo correction
Suggestion to have a bit more material on telescoping series
Merge pull request #22 from floydian/patch-1

Update root-test.tex
Some small edits