documentation updates

- fix typos/misspellings in documentation
- fix broken link on how to build Tvheadend
- standardize on most commonly used capitalization of "Tvheadend"
- update copyright year to 2013
- break up the handful of run-on lines
Merge remote-tracking branch 'origin/pr/254'
timeshift: fix bug that can cause failure when seeking hits start of file

this resulted in a failed read that terminated the timeshift buffer.