Implement Struct#values_at and Array#values_at .
Add API `mrb_get_values_at()` to mruby/range.h .
Delete unused variable in Array#delete_if
Fix indent
MSVC: treat implicit function decl. as error

As equivalent to GCC's `-Werror-implicit-function-declaration`.
add namespace prefix to `dump_irep`
mruby-math: define and use `Math::DomainError`

Domain errors are detected as per ISO C99 and may differ from CRuby.
Merge pull request #2173 from suzukaze/delete-unuse-variable

Delete unused variable in Array#delete_if
Merge pull request #2174 from suzukaze/fix-indent

Fix indent
Merge pull request #2176 from cremno/msvc-treat-implicit-function-declaration-as-error

MSVC: treat implicit function decl. as error
Merge pull request #2177 from cremno/math-domain-error

mruby-math: define and use `Math::DomainError`
Merge pull request #2178 from cremno/rename-dump_irep

add namespace prefix to `dump_irep`
remove each from range.c
Merge branch 'values_at' of https://github.com/take-cheeze/mruby into take-cheeze-values_at
raise TypeError instead of ArgumentError when argument of wrong type given to the values_at
do not raise error in mrb_range_beg_len()
convert range edges to integers
reindent else
Suppress warning when using readline in mirb.
Fix docs path.
use proper length for mrb_get_values_at()

separate mrb_range_beg_len() into two: the one truncates range into the
sequence size, and the one does not.  #values_at uses the latter.