Round when calculating frame delay

This has no effect on the current max fps of 30, since 1000/30 rounds
down to 13. However, 1000/60 is ~16.6666, so we need to round that up to
get a more accurate delay.
Set max fps to 60 and cut default speed in half
Use parse_duration() for durations that weren't using it

Also, parse_duration() no longer accepts ticks. An integer value with no
suffix is assumed to be in milliseconds.
Convert real time to ticks for animations
Get active frames working and implement Bresenham for some frame timing

There are still problems with active frames when animations are too
short.
Try to handle active frames for fast animations
Fix occasional black lines between tiles

Closes #1059
Merge pull request #1091 from dorkster/fixes

Fix occasional black lines between tiles
Fix compile a error

I am compiling with gcc 4.8.2 here and this error comes up
/home/sb/OSS/flare-engine/src/UtilsParsing.cpp: In function ‘int parse_duration(const string&)’:
/home/sb/OSS/flare-engine/src/UtilsParsing.cpp:58:51: error: could not convert ‘(((float)((int)MAX_FRAMES_PER_SEC *  val) / 1.0e+3f) + 5.0e-1f)’ from ‘float’ to ‘FPoint’
   val = floor(((val*MAX_FRAMES_PER_SEC) / 1000.f) + 0.5f);

The UtilsParsing.cpp file included the UtilsParsing.h header file, which
includes Utils.h where floor() seems to be defined for FPoint.

So we still need to include the math.h which works for the floats
we're using here.
Merge pull request #5 from stefanbeller/60fps_fix

Fix compile a error
Merge pull request #1090 from dorkster/60fps

Lock the engine at 60fps instead of 30fps
Remove unused variable.
Merge pull request #1093 from stefanbeller/remove_option_count

Remove unused variable.
Combine enemy and enemygroup layers

Closes #1089

Changes:
- the old 'enemy' map layer has been removed; the 'enemygroup' layer was
renamed to 'enemy' to replace it
- filenames are no longer used for placing enemies. Instead, use enemy
categories and the level property of groups to place specific enemies
- group level no longer requires a maximum value. The minimum is used
when it's missing
- the group area defaults to 1x1 if not defined
- the number of enemies in a group is 1 by default
- waypoints and wander_area only work for single enemies
- direction specifies the starting direction of the entire group
- requires_(not_)status now applies to enemy groups
Don't allow out-of-bounds values for variables in enemy groups
Merge remote-tracking branch 'upstream/master'
Add SDL2 to the INSTALL file

Tested on debian and fedora systems, the instructions for arch and windows
are untouched.
adapt .travis.yml continuous build integration for sdl2
Revert "adapt .travis.yml continuous build integration for sdl2"

travis doesn't have sdl2 yet apparently.

This reverts commit 99544132666572e90aa4b4e09e3ad7becf685d1f.
Run travis with sdl 1.2