Add small, generated version of language_sentiment_text [(#1660)](GoogleCloudPlatform/python-docs-samples#1660)

* Generated sample: language_sentiment_text

FYI generated from the following YAML GAPIC config:

  sample_value_sets:
    - id: analyze_sentiment
      title: "Analyzing Sentiment"
      description: "Proof of concept for analyzing sentiment"
      parameters:
        defaults:
        - document.type=PLAIN_TEXT
        - document.content="Your text to analyze, e.g. Hello, world!"
        attributes:
        - parameter: document.content
          sample_argument: true
      on_success:
      - define: sentiment=$resp.document_sentiment
      - print:
        - "Score: %s"
        - sentiment.score
      - print:
        - "Magnitude: %s"
        - sentiment.magnitude
    samples:
      standalone:
      - calling_forms: ".*"
        value_sets: analyze_sentiment
        region_tag: language_sentiment_text

* Add requirements.txt (not currently generated)

* Add test for language_sentiment_text (not currently generated)

* Move language_python_migration_document_text

Move language_python_migration_document_text so it uses a different snippet in preparation for deprecation of existing language_sentiment_text sample

* Rename generated snippets so filename == region tag

* Fix test for generated code sample (file rename to match region tag)

* Update Copyright year to 2018 in new hand-written file

* Fix lint errors of #language_sentiment_text test

* Regenerate #language_sentiment_text to fix lint errors (updated Python sample template)

* Binary string support in samples!

From PR googleapis/gapic-generator#2272

Author: beccasaurus

samples/snippets/snippets.py

@@ -39,12 +39,10 @@ def sentiment_text(text):
         text = text.decode('utf-8')
 
     # Instantiates a plain text document.
-    # [START language_python_migration_document_text]
     # [START language_python_migration_sentiment_text]
     document = types.Document(
         content=text,
         type=enums.Document.Type.PLAIN_TEXT)
-    # [END language_python_migration_document_text]
 
     # Detects sentiment in the document. You can also analyze HTML with:
     #   document.type == enums.Document.Type.HTML
@@ -87,9 +85,11 @@ def entities_text(text):
 
     # Instantiates a plain text document.
     # [START language_python_migration_entities_text]
+    # [START language_python_migration_document_text]
     document = types.Document(
         content=text,
         type=enums.Document.Type.PLAIN_TEXT)
+    # [END language_python_migration_document_text]
 
     # Detects entities in the document. You can also analyze HTML with:
     #   document.type == enums.Document.Type.HTML