ignore *.pdb
don't use of anonymous unions
remove deprecated register keyword
add MRB_INT_BIT
fix mrb_funcall calling
Merge pull request #1846 from take-cheeze/funcall_fix

Fix mrb_funcall calling.
Merge pull request #1843 from take-cheeze/suppress_warnings

Suppress warnings.
avoid mrb_string_value_cstr() to copy string between mrb_states in tests
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