problems with pdb documentation

[prjemian]

Problems with reST syntax in PR #614 (and issue #553)

NeXus/definitions/build/manual/source/classes/base_classes/NXpdb.rst:50: SEVERE: Unexpected section title or transition.

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NeXus/definitions/build/manual/source/classes/base_classes/NXpdb.rst:54: ERROR: Unexpected indentation.
NeXus/definitions/build/manual/source/classes/base_classes/NXpdb.rst:55: WARNING: Block quote ends without a blank line; unexpected unindent.
NeXus/definitions/build/manual/source/classes/base_classes/NXpdb.rst:68: SEVERE: Unexpected section title or transition.

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NeXus/definitions/build/manual/source/classes/base_classes/NXpdb.rst:72: SEVERE: Unexpected section title or transition.

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NeXus/definitions/build/manual/source/classes/base_classes/NXpdb.rst:86: SEVERE: Unexpected section title or transition.

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NeXus/definitions/build/manual/source/classes/base_classes/NXpdb.rst:55: ERROR: Unknown target name: "loop".

[prjemian]

when showing computer code in reST, need to use "::" on preceding line of prose, then indent the computer code, such as this line of reST

the following code shows how to document computer code::

    print("Hello, world.")

which renders like this:

---

the following code shows how to document computer code::

    print("Hello, world.")

[zjttoefs]

Since this will be merged when #614 is merged it can be closed.