ENH: PV linking via DOL/OMSL + CPP input link

[klauer]

Closes #166

I think this could pair with an lcls-twincat-general set of structures, as indicated in the issue.

cc @ghalym

[codecov-io]

Codecov Report

Merging #167 into master will increase coverage by 0.26%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #167      +/-   ##
==========================================
+ Coverage   79.57%   79.83%   +0.26%     
==========================================
  Files          18       18              
  Lines        2208     2237      +29     
==========================================
+ Hits         1757     1786      +29     
  Misses        451      451

Impacted Files	Coverage Δ
pytmc/pragmas.py	96.42% <100%> (+0.09%)	:arrow_up:
pytmc/bin/pragmalint.py	84.93% <100%> (+0.56%)	:arrow_up:
pytmc/record.py	94.62% <100%> (+0.37%)	:arrow_up:

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[klauer]

Also need to add some FBs to lcls-twincat-general that support this easily

[klauer]

Most recent commit allows for chaining of link: ... pragmas, such that the following is possible:

    {attribute 'pytmc' := '
        pv: TEST
        link: PV_TO_LINK_TO
    '}
    fbTest : FB_LREALFromEPICS;

FUNCTION_BLOCK FB_LREALFromEPICS
VAR
    {attribute 'pytmc' := '
        pv: FromEPICS
        link:
    '}
    fFromEPICS : LREAL;

    {attribute 'pytmc' := '
        pv: FromEPICS:Sevr
        link: .SEVR
    '}
    iSeverityFromEPICS : INT;