Wrapped quick_xml::error in a new type to hide quick_xml

[Ochism]

Should close #62
Though I wonder if ToXml's return of quick_xml::Error might also need to be removed

[codecov]

Codecov Report

Merging #65 (33f939f) into master (9956e1b) will decrease coverage by 4.52%.
The diff coverage is 60.38%.

❗ Current head 33f939f differs from pull request most recent head 02d8dbe. Consider uploading reports for the commit 02d8dbe to get more accurate results

@@            Coverage Diff             @@
##           master      #65      +/-   ##
==========================================
- Coverage   85.08%   80.56%   -4.53%     
==========================================
  Files          19       19              
  Lines        1301     1415     +114     
==========================================
+ Hits         1107     1140      +33     
- Misses        194      275      +81     

Impacted Files	Coverage Δ
src/error.rs	0.00% <0.00%> (ø)
src/extension/util.rs	75.92% <40.00%> (-17.41%)	⬇️
src/text.rs	67.90% <44.00%> (-12.10%)	⬇️
src/entry.rs	75.20% <50.00%> (-4.80%)	⬇️
src/person.rs	71.42% <50.00%> (-9.13%)	⬇️
src/source.rs	71.81% <50.00%> (-5.33%)	⬇️
src/toxml.rs	78.57% <50.00%> (-9.43%)	⬇️
src/feed.rs	79.26% <57.14%> (-4.74%)	⬇️
src/extension/mod.rs	70.96% <66.66%> (-5.04%)	⬇️
src/generator.rs	79.06% <70.58%> (-8.03%)	⬇️
... and 12 more

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