Closes #250 (issue with reference links on first pass)

[tlienart]

This closes #250. The issue was simple, the function jd2html which is the barebone converter from markdown to html is called in add_rss_item passing a keyword indicating that the call is internal.

However jd2html didn't pass that indication to convert_md which then assumed that this was a new page it was on and, as a result, flushed out dictionaries including the dictionary of reference links. As a result when trying to fix links, JuDoc saw an empty reference dictionary and assumed that these links were not links after all and so just outputted them as such.

[codecov]

Codecov Report

Merging #253 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #253      +/-   ##
==========================================
- Coverage   90.67%   90.66%   -0.01%     
==========================================
  Files          29       29              
  Lines        1437     1436       -1     
==========================================
- Hits         1303     1302       -1     
  Misses        134      134

Impacted Files	Coverage Δ
src/JuDoc.jl	100% <ø> (ø)	⬆️
src/manager/file_utils.jl	82.69% <ø> (-1.24%)	⬇️
src/converter/md.jl	98.29% <100%> (ø)	⬆️
src/converter/html.jl	96.77% <100%> (ø)	⬆️
src/converter/link_fixer.jl	100% <100%> (ø)

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