NLPCloud client integration (#81)

lots of kwargs! generation docs here:
https://docs.nlpcloud.com/#generation

This somewhat breaks the paradigm introduced in LLM base class as the
stop sequence isn't a list, and should rightfully be introduced at the
time of initialization of the class, along with the other kwargs that
depend on its presence (e.g. remove_end_sequence, etc.) curious if you'd
want to refactor LLM base class to take out stop as a specific named
kwarg?

tests/integration_tests/llms/test_nlpcloud.py

@@ -0,0 +1,10 @@
+"""Test NLPCloud API wrapper."""
+
+from langchain.llms.nlpcloud import NLPCloud
+
+
+def test_nlpcloud_call() -> None:
+    """Test valid call to nlpcloud."""
+    llm = NLPCloud(max_length=10)
+    output = llm("Say foo:")
+    assert isinstance(output, str)