lib: move internal packages to lib/internal and export ParseDockerURL and annotations

[iaguis]

Good things brought by this PR:

• Internal functions are clearly separated from the rest
• People can use annotations from outside docker2aci
• We weren't exporting ParseDockerURL which is used by rkt, fix that

Fixes #133

[krnowak]

This is troublesome - the returned result is a part of internal package, so the user of the ParseDockerURL function can use it directly, but cannot write a function that takes the *types.ParsedDockerURL, because the user will not be able to import the internal package…

I think that putting the ParsedDockerURL struct in the common package will end up in cyclic dependencies again, so consider adding type ParsedDockerURL types.ParsedDockerURL somewhere in the common package and do some casting in the ParseDockerURL function.

[krnowak]

Something to consider before releasing 1.0 in a separate PR - replace the pkg/log with a Logger field in the CommonConfig struct, so users can pass their own logger. The Logger fields would be of some interface type like:

type Logger interface {
    Debug(i ...interface{})
    Info(i ...interface{})
}

so the implementer could implement the Debug function in the same way as currently pkg/log does without resorting to some global boolean variable set by the InitDebug() function. Possibly export two implementation like DefaultLogger with configurable debugging function and DevNullLogger.

[krnowak]

Alright, I think I'll put my comment into a separate issue.

LFAD.

[krnowak]

Filed #136.

[iaguis]

Thanks!