Added a short description on how to add mruby gems to the compilation workflow.
Merge pull request #1848 from joejimbo/master

Added a short description about mruby gems
Merge pull request #1826 from unak/mswin

ignore *.pdb
add mrb_strlen_lit which makes _lit macros safer

strlen(3) + string literal is usually optimized but strlen(3) doesn't
check if its argument is really a string literal. This is important for
mruby's _static functions to which some _lit macros are expanded (string
literals have static storage). See comment for some additional info.

remove unnecessary parentheses
add including limits.h.

Because Android's libc(bionic) defines SIZE_MAX at limits.h.
Merge pull request #1850 from cremno/safer-lit-macros

add mrb_strlen_lit
Merge pull request #1851 from tmash06/add_include_limit_h

add including limits.h.
Merge pull request #1849 from cremno/add-mrb_int_bit-macro

add MRB_INT_BIT
peephole optimization for OP_JMP{IF,NOT}
too much optimization
add mruby-enumerator
mruby-enumerator: move definitions in core_mod.rb to mrblib core
remove ambiguity warnings
move dependency check from runtime to mrbgem.rake
remove new_label(s) where label position can be obtained from genop()
fix compile error check of Mrbc command
Merge pull request #1855 from take-cheeze/fix_mrbc_compile_error

Fix compile error check of Mrbc command.
Merge branch 'master' of github.com:mruby/mruby
Don't redefine timeval on MingW64 environments
Merge pull request #1857 from mitchellh/f-fix-mingw-time

Don't redefine timeval in MinGW environments