tree 3d87223317cd15c2fc3dff0f71643dc0ca531533
parent c8c6312ace53b92403a66e61ba81898f092cabe5
author akutz <sakutz@gmail.com> 1447359640 -0600
committer Steve Francia <steve.francia@gmail.com> 1450970647 -0500

Adds MergeConfig functionality

This patch adds the `MergeConfig` and `MergeInConfig` functions to
enable reading new configuration files via a merge strategy rather
than replace. For example, take the following as the base YAML for a
configuration:

    hello:
        pop: 37890
        world:
        - us
        - uk
        - fr
        - de

Now imagine we want to read the following, new configuration data:

    hello:
        pop: 45000
        universe:
        - mw
        - ad
    fu: bar

Using the standard `ReadConfig` function the value returned by the
nested key `hello.world` would no longer be present after the second
configuration is read. This is because the `ReadConfig` function and
its relatives replace nested structures entirely.

The new `MergeConfig` function would produce the following config
after the second YAML snippet was merged with the first:

    hello:
        pop: 45000
        world:
        - us
        - uk
        - fr
        - de
        universe:
        - mw
        - ad
    fu: bar

Examples showing how this works can be found in the two unit tests
named `TestMergeConfig` and `TestMergeConfigNoMerge`.