Minor code cleanup (formatting)
[FIX] Detect 32/64 bit on Windows, to download Android NDK

Grabbed the answer from StackOverflow, and should work for other OSes too, but kept for Windows only.
Merge pull request #62 from alanjds/patch-1

[FIX] Detect 32/64 bit on Windows, to download Android NDK
Added env var querying for default and bool
Added env var checking to all config get methods.

The new method replaces the manual env var parsing with simply setting
the config's value to the env var value. This lets the normal parsing
methods do the work later, to avoid duplication of effort.
Added env check during config build
Added a few comments and formatting changes
Added app.p4a_dir token
Variable renaming for clarity
Added check for package name starting with number
Rearranged package.name check to avoid crash

Buildozer would previously crash if a package name was '', as it checked
for zero length *and* tried to check if the first character was a
number.
correctly check requirements if a specific version is used (package==version will check the requirement only on package, not the full requirement token.)
Merge branch 'master' of ssh://github.com/kivy/buildozer
Clarified wording in README
Merge pull request #65 from inclement/packagename

Check for package name starting with number
Merge pull request #75 from inclement/readme3

Clarified wording in README
Add bin to suggested default directory excludes

Prevent packaging apks in apks in apks...
Merge pull request #78 from josephlee021/master

Add 'bin' to suggested default directory excludes
Merge pull request #60 from inclement/p4a

Add ability to choose python-for-android directory
Delete dist dir if running distribute.sh