Add the formatter concept to agent config.

Add the formatter concept to agent config.

In order to decouple the internal structure of the agent config from how it is
stored on disk, we introduce formatters.  They are responsible for moving the
internal config to and from a serialization format.

The existing format is called "format 1.12", as that is the stable release
that the format was introduced.

Some of the methods are purposefully trivial at this stage, and they are
flushed out in the next branch.

https://code.launchpad.net/~thumper/juju-core/agent-config-formatters/+merge/183074

(do not edit description out of merge proposal)

[thumper, 2013-08-30 05:51:53]

Please take a look.

[fwereade, 2013-08-30 07:06:22]

LGTM, just quibbles

https://codereview.appspot.com/13237050/diff/1/agent/format-1.12.go
File agent/format-1.12.go (right):

https://codereview.appspot.com/13237050/diff/1/agent/format-1.12.go#newcode19
agent/format-1.12.go:19: const format112 = "format 1.12"
1_12 throughout?

https://codereview.appspot.com/13237050/diff/1/agent/format-1.12_whitebox_tes...
File agent/format-1.12_whitebox_test.go (right):

https://codereview.appspot.com/13237050/diff/1/agent/format-1.12_whitebox_tes...
agent/format-1.12_whitebox_test.go:6: // package.
I don't personally feel we need to make a big deal out of this.

[thumper, 2013-09-02 04:03:19]

Please take a look.

https://codereview.appspot.com/13237050/diff/1/agent/format-1.12.go
File agent/format-1.12.go (right):

https://codereview.appspot.com/13237050/diff/1/agent/format-1.12.go#newcode19
agent/format-1.12.go:19: const format112 = "format 1.12"
On 2013/08/30 07:06:22, fwereade wrote:
> 1_12 throughout?

I have renamed "format112" to "format_1_12" because "format1_12" looked too
weird.

https://codereview.appspot.com/13237050/diff/1/agent/format-1.12.go#newcode22
agent/format-1.12.go:22: type formatter112 struct {
formatter112 becomes formatter_1_12

https://codereview.appspot.com/13237050/diff/1/agent/format-1.12.go#newcode26
agent/format-1.12.go:26: type format112Serialization struct {
format112Serialization becomes format_1_12Serialization

https://codereview.appspot.com/13237050/diff/1/agent/format-1.12_whitebox_tes...
File agent/format-1.12_whitebox_test.go (right):

https://codereview.appspot.com/13237050/diff/1/agent/format-1.12_whitebox_tes...
agent/format-1.12_whitebox_test.go:6: // package.
On 2013/08/30 07:06:22, fwereade wrote:
> I don't personally feel we need to make a big deal out of this.

Removed then.