Add logic to deal with reflect pkg changes on tip.

This commit adds logic to gracefully handle the new internal reflect.Value
structure on tip as of golang commit ecccf07e7f9d.  It accomplishes this
by doing some inspection at init time and choosing the appropriate offsets
as well as modifying which offset is used for the value accordingly.  As a
result, this allows spew to work properly with both the current release
version of Go as well as tip.

Fixes #15.
Update TravisCI to use Go 1.2.

Also fix a comment typo in doc.go under the custom formatter section.
Setup TravisCI to report cov stats to coveralls.io.
Configure TravisCI goveralls call correctly.

By default goveralls tries to use gocov.  This modifies it to use the
cover profile provided by go test instead.
Correct TravisCI .yml file.
Don't change to spew dir before invoking goveralls.
Add coveralls.io test coverage badge.
Configure TravisCI to test with testcgo tag.
Point test coverage badge at master branch.
Dump non-zero len and cap for applicable types.

Closes #16.