Add PVA support

[thomascobb]

Docs build currently failing until a production release of epicscorelibs is available and can be pulled down to DLS to updated Pipfile.lock.

Still needs some tests writing when p4p is released against the same epicscorelibs prod release

Refs https://github.com/mdavidsaver/epicscorelibs/issues/13

[codecov]

Codecov Report

Merging #17 (36e5d39) into master (94d2e66) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #17      +/-   ##
==========================================
- Coverage   82.05%   82.03%   -0.03%     
==========================================
  Files          13       13              
  Lines         797      796       -1     
==========================================
- Hits          654      653       -1     
  Misses        143      143              

Impacted Files	Coverage Δ
softioc/imports.py	94.00% <ø> (-0.24%)	⬇️
softioc/softioc.py	89.24% <ø> (ø)
softioc/__init__.py	91.66% <100.00%> (+0.75%)	⬆️

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