Page errors 83

Addresses Issue #83.

Page errors can now be logged and traced.

Additions:
- errors metric.
- addError() method separate from addNotice()
- results.errors array
- logging of results.errors after results.notices.

Depending on appropriateness, page error traces in --format=normal might need to be restricted to --verbose mode only.

Test URLs:

http://www.samsung.com (Race Condition, should be 2 errors)
http://www.verizon.com (Syntax Error, 1 error)