For instance, by appending code to the Pods prefix header.

Require FileUtils

Update example podfiles to current format. Maybe it’s better to have a separate API/DSL for a podfile after all, so that this isn't necessary.

Add Specification#clean_paths to specify paths to remove after downloading

For example, a library could have documentation, tests, example files, or other files
which are not relevant for the purpose of using the library and can be removed after downloading.

Add per podspec compiler flags support and Specification#requires_arc shortcut

By default use the same header dir for pod that are part of another pod. This can be changed by specifiying a custom `header_dir`. Closes #14.

Copy headers to the pod's header dir $(BUILT_PRODUCTS_DIR)/Pods/PodName by default, but allow for customization by overriding copy_header_mapping(s).

In progress work to close Issue 14, the directory structure is now preserved for headers being copied in, need to update specs to match