README.md

This patch add several deprecate warnings to FreeIPABaseModule, and
creates adapters to ease conversion of client classes to
IPAAnsibleModule.

There is no 'ipa_commands' management in IPAAnsibleModule, as 'command's
is a list of tuples containing '(command, name, args)', and should be
managed by the module itself. Commands with no arguments should use an
empty dictionary as 'args'.

The 'ipa_run' method should be replaced by:

```
exit_args = {}
ipaapi_context = self.params_get("ipaapi_context")
with self.ipa_connect(context=ipaapi_context):
    self.check_ipa_params()
    self.define_ipa_commands()
    changed = self.execute_ipa_commands(
                self.ipa_commands,
                result_handler=my_custom_handler,
                exit_args=exit_args
            )
self.exit_json(changed=changed, **exit_args)
```

The 'process_command_result' method should be changed to a result
handler:

```
def my_result_handler(self, result, command, name, args, exit_args):
    """Process command result.""'
```

Use of 'ipa_params' should be replaced by IPAAnsibleModule.params_get.
If 'get_ipa_command_args' is used, then the mapping can be created with
class IPAParamMapping (formelly AnsibleFreeIPAParams), which also
enables the same property-like usage of 'ipa_params':

```
param_mapping = IPAParamMapping(module, mapping)
```

The goal is to have all ansible-freeipa modules using the same codebase,
reducing code duplication, and allowing better object composition, for
example, with the IPAParamMapping class.