Increase default minimum API level to 10

While nearly all available today features important for games were included in
API level 9, because it:

 - added concurrent garbage collector
 - added new input sensors used often in games (gyroscope, linear acceleration)
 - completed OpenGL ES 2.0 with earlier missing glDrawElements and
   glVertexAttribPointer
 - added xlarge screens
 - added NativeActivity
 - added NFC
 - copies whole data at once when creating FloatBuffer like desktop Java,
   instead of doing it one by one like earlier Android API versions (massive
   performance gain for games)

There seems to be several reasons to use API level 10 instead:

 - Google silently omits link to this version of API (API 9 is said to have
   serious bugs, but I'm unaware what they are)
 - Google does not distribute SDK platform files for API 9 so we cannot test
   apps in emulator
 - It is very very hard to find device with API 9, only 0.1% of devices use it
   vs 36.4% of API 10 devices out there
 - API 10 came 3 months after API 9 and most if not all devices were compatible
   and upgraded
 - we are speaking about default, so if someone wants, he can lover it even to
   API 3, 4, 7 or 8
Merge pull request #25 from aginiewicz/higher-min-sdk

Increase default minimum API level to 10