feat: add read-only support of the meta API (#13)

* Add bases API.

* Implement get tables schema

* Rename GetBase to GetBaseSchema

* Add tests

* Update doc

testdata/get_bases.json

@@ -0,0 +1,15 @@
+{
+  "bases": [
+    {
+      "id": "appLkNDICXNqxSDhG",
+      "name": "Apartment Hunting",
+      "permissionLevel": "create"
+    },
+    {
+      "id": "appSW9R5uCNmRmfl6",
+      "name": "Project Tracker",
+      "permissionLevel": "edit"
+    }
+  ],
+  "offset": "itr23sEjsdfEr3282/appSW9R5uCNmRmfl6"
+}