This requires a parameter to be accepted by the block passed to
Geocoder.configure, which means you don't need to remember that the
method is called "config"--you can call it whatever you want.
This behavior seems more standard for configuration blocks.

Change :request_headers to :http_headers (for consistency).

It's not an ideal name either, but it's short and it's slightly more
specific than "method".

Instead use an array for key, client, and channel.

Removed set_defaults from all tests and replaced with teardown to reset the defaults.

Signed-off-by: James McCarthy <james2mccarthy@gmail.com>

Configurations changed to provide a DSL (similar to Rails) to configure Geocoder. A singleton pattern was used to allow the code *Geocoder.configure { |config| ... }*, and delegation was used to maintain compatibility. New configuration options (units and method) for calculations were implemented, with default value: km and spherical, respectively.

Allows custom handling of geocoding service connection problems.

Instead use a proxy if http_proxy or https_proxy is set. Also revise
code style to be more consistent with rest of library.

Geocoder will try to use environment's http_proxy or https_proxy when doing lookups unless that behaviour has been disabled in the configuration

Now that we also support an API key for Google it makes sense for this to
be generic.

Just set Geocoder::Configuration.cache to any key/value store that
implements #[], #[]=, and #keys. You can also set
Geocoder::Configuration.cache_prefix to use a custom prefix for keys.

Add implementation for Google and anticipate addition of Yahoo (supply
config option).