fix memcpy-param-overlap
temporary macros for checked arithmetic functions
add function for checked mrb_int addition
add function for checked mrb_int subtraction
Implement day of week methods.
Merge pull request #2199 from cremno/use-memmove

fix memcpy-param-overlap
Merge pull request #2201 from take-cheeze/day_of_week

Implement day of week methods.
Merge pull request #2200 from cremno/add-functions-for-safe-addition-and-subtraction

Add functions for safe addition and subtraction
refactor fix_mod

fix unreachable condition
use b
Merge pull request #2202 from akuroda/pr_refactor_fix_mod

refactor fix_mod
Add a comment to ObjectSpace.each_object.
Merge pull request #2203 from yui-knk/add-call-seq

Add a comment to ObjectSpace.each_object.