Catch up to TMX Format as of Tiled 0.12

[georgeraraujo]

and report map attributes in the test program.

Now that tmxparser is feature complete, I also suggest to release version 1.12 (1 being the last release of tmxparser, and 0.12 being the current Tiled release) after changing src/Tmx.h accordingly:

#define TMX_PARSER_VERSION_MAJOR 1
#define TMX_PARSER_VERSION_MINOR 12

I should also mention that tmxparser goes down in flames when an <image> element does not include the width and height attributes, which are optional; line 167 of TmxTileset.cpp incorrectly assumes that those were parsed even when they were not, causing a crash in line 187 when trying to index into a zero-length vector. Instead of hacking something, I think it's about time to put error checking and assertions all over the place.

[andrewrk]

Alrighty. I tagged release 2.0.0. The major version is bumped from 1.0.0 because there were changes made to the API and we're following semver (as per #21)

[georgeraraujo]

Sounds good to me.

I just opened a pull request to move the version number to configured header file Tmx.h.in, since Tmx.h was left untouched as of 2.0.0 and incorrectly reports

#define TMX_PARSER_VERSION_MAJOR 1
#define TMX_PARSER_VERSION_MINOR 0