doc: improve embedding functions documentation (#983)

Got some user feedback that the `implicit` / `explicit` distinction is
confusing.
Instead I was thinking we would just deprecate the `with_embeddings` API
and then organize working with embeddings into 3 buckets:

1. manually generate embeddings
2. use a provided embedding function
3. define your own custom embedding function

python/lancedb/embeddings/utils.py

@@ -26,7 +26,7 @@ import pyarrow as pa
 from lance.vector import vec_to_table
 from retry import retry
 
-from ..util import safe_import_pandas
+from ..util import deprecated, safe_import_pandas
 from ..utils.general import LOGGER
 
 pd = safe_import_pandas()
@@ -38,6 +38,7 @@ IMAGES = Union[
 ]
 
 
+@deprecated
 def with_embeddings(
     func: Callable,
     data: DATA,

python/lancedb/util.py

@@ -11,9 +11,11 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 
+import functools
 import importlib
 import os
 import pathlib
+import warnings
 from datetime import date, datetime
 from functools import singledispatch
 from typing import Tuple, Union
@@ -239,3 +241,25 @@ def _(value: list):
 @value_to_sql.register(np.ndarray)
 def _(value: np.ndarray):
     return value_to_sql(value.tolist())
+
+
+def deprecated(func):
+    """This is a decorator which can be used to mark functions
+    as deprecated. It will result in a warning being emitted
+    when the function is used."""
+
+    @functools.wraps(func)
+    def new_func(*args, **kwargs):
+        warnings.simplefilter("always", DeprecationWarning)  # turn off filter
+        warnings.warn(
+            (
+                f"Function {func.__name__} is deprecated and will be "
+                "removed in a future version"
+            ),
+            category=DeprecationWarning,
+            stacklevel=2,
+        )
+        warnings.simplefilter("default", DeprecationWarning)  # reset filter
+        return func(*args, **kwargs)
+
+    return new_func