charm: do not verify bundles on read

We have the BundleData.Verify method for that.
Clients can then decide for themselves whether to
verify the bundle data with charms or not.
Add a const for default testing charm series.
Merge pull request #34 from tasdomas/default-series-const

Add a const for default testing charm series.
add dev-version warning
adjust README
Merge pull request #37 from rogpeppe/012-no-verify-on-bundle-read

charm: do not verify bundles on read
charm: complain about missing schema
Merge pull request #38 from rogpeppe/013-missing-schema-error

charm: complain about missing schema
Updating to gopkg.in path for bugfix.
Merge pull request #39 from katco-/goyaml-update

Goyaml update
remove "unstable version" notice from README.md
Merge pull request #40 from rogpeppe/014-stable

remove "unstable version" notice from README.md
Added a collect-metrics hook.
Merge pull request #44 from tasdomas/collect-metrics-hook

Added a collect-metrics hook.
Prefer io.Copy to needless allocation

When a charm has large files in it, reading the entire file into memory
is wasteful. When processing many charms it can cause GC problems.
Merge pull request #45 from jrwren/v3

Prefer io.Copy to needless allocation
charm: close file after opening
Merge pull request #46 from rogpeppe/015-close

charm: close file after opening