Case insensitive doctype

[leondzn]

Some sources return doctype definitions in lowercase triggering the "Unterminated comment" error like on issue #80. I've made the check case insensitive.

[codecov-io]

Codecov Report

Merging #110 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #110      +/-   ##
============================================
+ Coverage     63.64%   63.64%   +<.01%     
- Complexity     1162     1164       +2     
============================================
  Files           237      237              
  Lines          4252     4253       +1     
  Branches       1021     1022       +1     
============================================
+ Hits           2706     2707       +1     
  Misses          897      897              
  Partials        649      649

Impacted Files	Coverage Δ	Complexity Δ
...e/src/main/java/com/tickaroo/tikxml/XmlReader.java	72.79% <100%> (+0.07%)	119 <3> (+2)	⬆️

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[sockeqwe]

Thanks!