Added StartIndex and EndIndex to MessageTemplateToken
Use the new constructors when parsing
Added indexes to test tokens
Added more tests to improve coverage
Added missing XML docs
Removed EndIndex property
Made startIndex ctor argument optional
Brought net40 project up to par
Changed default value back to -1
Merge pull request #249 from khellang/property-tag-indexes

[WIP] Added StartIndex and EndIndex to MessageTemplateToken