array.rb: refactor some code

irep dump: fix format string for MRB_USE_FLOAT

delete duplicate definition of Exception.exception

It overwrote the original definition in src/error.c, line 446.

IEC 60559 single format has 6 to 9 significant decimal digits precision.

However the printf conversion specifier e (and E, of course) already
writes 1 digit - the one before the decimal point - and precision
specifies the number of digits to write after the decimal point.

Remove duplicated RARRAY_LEN check in ary_elt

Remove non-need tmp value in mrb_obj_to_sym

Add build on Trusty and OS X

The default 6.1 was slow

be able to source with :path for mrbgems

pop cmdarg in lambda body; fix [ruby-bug#11380]

regression introduced by 2fe556d9

mrbgem compile should be depend on mrbgem.rake

Shallow clone mgem source

update mrbgems doc

fix android compile bug : uninitialized constant GCC_VERSION

Add ability to change compiler versions for androideabi