Add provider info functions to the FFI API

A lot of work from @Hocuri and @Simon-Laux mostly.

This exposes the API of the deltachat-provider-overview crate on the
deltachat FFI API, allowing clients to use it to help users set up
their accounts.

python/src/deltachat/provider.py

@@ -0,0 +1,67 @@
+"""Provider info class."""
+
+from .capi import ffi, lib
+from .cutil import as_dc_charpointer, from_dc_charpointer
+
+
+class ProviderNotFoundError(Exception):
+    """The provider information was not found."""
+
+
+class Provider(object):
+    """Provider information.
+
+    :param domain: The domain to get the provider info for, this is
+    normally the part following the `@` of the domain.
+    """
+
+    def __init__(self, domain):
+        provider = ffi.gc(
+            lib.dc_provider_new_from_domain(as_dc_charpointer(domain)),
+            lib.dc_provider_unref,
+        )
+        if provider == ffi.NULL:
+            raise ProviderNotFoundError("Provider not found")
+        self._provider = provider
+
+    @classmethod
+    def from_email(cls, email):
+        """Create provider info from an email address.
+
+        :param email: Email address to get provider info for.
+        """
+        return cls(email.split('@')[-1])
+
+    @property
+    def overview_page(self):
+        """URL to the overview page of the provider on providers.delta.chat."""
+        return from_dc_charpointer(
+            lib.dc_provider_get_overview_page(self._provider))
+
+    @property
+    def name(self):
+        """The name of the provider."""
+        return from_dc_charpointer(lib.dc_provider_get_name(self._provider))
+
+    @property
+    def markdown(self):
+        """Content of the information page, formatted as markdown."""
+        return from_dc_charpointer(
+            lib.dc_provider_get_markdown(self._provider))
+
+    @property
+    def status_date(self):
+        """The date the provider info was last updated, as a string."""
+        return from_dc_charpointer(
+            lib.dc_provider_get_status_date(self._provider))
+
+    @property
+    def status(self):
+        """The status of the provider information.
+
+        This is one of the
+        :attr:`deltachat.const.DC_PROVIDER_STATUS_OK`,
+        :attr:`deltachat.const.DC_PROVIDER_STATUS_PREPARATION` or
+        :attr:`deltachat.const.DC_PROVIDER_STATUS_BROKEN` constants.
+        """
+        return lib.dc_provider_get_status(self._provider)