Add documentation for all VariantHeader-related classes (PR #1394)

Author: TimD1

doc/api.rst

@@ -213,15 +213,27 @@ VCF/BCF files
 .. autoclass:: pysam.VariantHeader
    :members:
 
+.. autoclass:: pysam.VariantHeaderMetadata
+   :members:
+
 .. autoclass:: pysam.VariantMetadata
    :members:
 
+.. autoclass:: pysam.VariantHeaderRecords
+   :members:
+
 .. autoclass:: pysam.VariantHeaderRecord
    :members:
 
+.. autoclass:: pysam.VariantHeaderContigs
+   :members:
+
 .. autoclass:: pysam.VariantContig
    :members:
 
+.. autoclass:: pysam.VariantHeaderSamples
+   :members:
+
 .. autoclass:: pysam.VariantRecord
    :members: