Add missing Algorithm Usage examples

[NickDraper]

This issue was originally TRAC 9920

This ticket is blocks : TRAC7517

The following algorithms were found to be missing usage examples or have no rst file at all.

The outstanding documentation tickets were checked, but a match could not be found, so these appear to be missed.

1. LoadMuonNexus
2. UserFunction1D
3. LoadQKK
4. Lorentzian1D

Please add a usage example wherever possible

[NickDraper]

@KarlPalmen (2014-09-23T15:06:24):
LoadQKK also has a missing description http://trac.mantidproject.org/mantid/ticket/9190.

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@NickDraper (2014-12-08T10:25:35):
Moved to the backlog at the code freeze of R3.3

[KarlPalmen]

LoadMuonNexus now has usage examples at http://docs.mantidproject.org/nightly/algorithms/LoadMuonNexus-v2.html#usage

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