feat: rename crates from gejdr-crud to georm

This commit renames gejdr-crud to georm for an easier name to remember
in case I publish `georm` and `georm-macros`. This commit extracts the
`Georm` (formerly `Crud`) trait from `gejdr-core` to its dedicated
crate `georm` on which gejdr-core now depends.

Currently writing tests

georm/tests/simple_struct.rs

@@ -0,0 +1,9 @@
+use georm::Georm;
+
+#[derive(Debug, Georm)]
+#[georm(table = "tests.authors")]
+struct Author {
+    #[georm(column = "author_id", id)]
+    id: i32,
+    name: String
+}