build fix for mac os:
1) type_info visibility for CatapultAttack
2) using IObjectInfo::CArmyStructure in min_element : operator< should be const
another build fix:
Undefined symbols for architecture x86_64:
  "operator<<(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, EVictoryLossCheckResult const&)
Merge pull request #20 from Haryaalcar/develop

build fixes for mac os
Fixed path to header in ERM module
Replaced usage of DLL_LINKAGE with ELF_VISIBILITY in netpacks. Please make sure that compilation now works on all platforms
fix mingw build
add comment. no code changes.
Renamed readme to readme.md to enable formatting in github UI
Compatiblity for last version of Cove (and likely any other town mods)
[ERM] Fix build
* update project
Merge pull request #2 from vcmi/develop

Merge upstream changes