Update androidndk.rake to add support 64bit architectures.

'mips64' can integrate into 'mips'.
'x86_64' is the same as 'mips64'.

This is the first step of implementing 'ldflags'.

WIP - New Android NDK toolchain

point to the right compile file

fix `rake doc` error

using mrbdoc

Simpler documentation

print unicode on windows console