Zeeklings screech and have curved flight path

[wbrawner]

• Added new screech sound
• Track Zeekling's and player's positions before diving
• Modified Zeeklings y velocity on dive based on distance they've moved

I'm not so sure about the math here, so any suggestions on how to improve it would be very welcome. Also, the screech sound came from here: https://opengameart.org/content/15-monster-gruntpaindeath-sounds There's a link there to the publication of the sounds in which the author says the sounds are free to use but he requests attribution: http://cubeengine.com/forum.php4?action=display_thread&thread_id=2164 so I'm not sure if this can be used here or not but I figured I'd give it a shot anyways

[mention-bot]

@wbrawner, thanks for your PR! By analyzing the history of the files in this pull request, we identified @tobbi and @Hume2 to be potential reviewers.

[wbrawner]

This might be the sound designer: http://michel-baradari.de/ could be worth it to contact him and check if he's cool with us using the sound, though we might need a German speaker to do that :D

[maxteufel]

The CC-BY license as specified on OpenGameArt is perfectly fine and similar to the licenses we use for other stuff. German wouldn't be a problem though.

[tobbi]

/Users/travis/build/SuperTux/supertux/src/badguy/zeekling.cpp:197:11: error: unused variable 'distance_to_travel' [-Werror,-Wunused-variable]

      int distance_to_travel = pre_dive_pos.y - pre_dive_player_pos.y;

          ^

1 error generated.

make[2]: *** [CMakeFiles/supertux2_lib.dir/src/badguy/zeekling.cpp.o] Error 1

make[1]: *** [CMakeFiles/supertux2_lib.dir/all] Error 2

make: *** [all] Error 2

[wbrawner]

Took out the unused variable. Still working on the math for the curve

[tobbi]

/home/travis/build/SuperTux/supertux/src/badguy/zeekling.cpp: In constructor ‘Zeekling::Zeekling(const ReaderMapping&)’:

/home/travis/build/SuperTux/supertux/src/badguy/zeekling.cpp:28:1: error: ‘Zeekling::pre_dive_pos’ should be initialized in the member initialization list [-Werror=effc++]

 Zeekling::Zeekling(const ReaderMapping& reader) :

 ^

/home/travis/build/SuperTux/supertux/src/badguy/zeekling.cpp:28:1: error: ‘Zeekling::pre_dive_player_pos’ should be initialized in the member initialization list [-Werror=effc++]

/home/travis/build/SuperTux/supertux/src/badguy/zeekling.cpp: In constructor ‘Zeekling::Zeekling(const Vector&, Direction)’:

/home/travis/build/SuperTux/supertux/src/badguy/zeekling.cpp:40:1: error: ‘Zeekling::pre_dive_pos’ should be initialized in the member initialization list [-Werror=effc++]

 Zeekling::Zeekling(const Vector& pos, Direction d) :

 ^

/home/travis/build/SuperTux/supertux/src/badguy/zeekling.cpp:40:1: error: ‘Zeekling::pre_dive_player_pos’ should be initialized in the member initialization list [-Werror=effc++]

[christ2go]

@wbrawner Do you still intend to work on this?

[wbrawner]

Sorry, I've been pretty absent here. I don't really have the time to work on this any time soon and I haven't since I opened the PR, so I'll just close this for now.