Merge pull request #2182 from cremno/use-isfinite

simply use `isfinite`
Merge pull request #2183 from yui-knk/fix-error-comment

Fix comment of exc_inspect (and adjust spaces)
Fix typo.
Add Hash comments
Merge pull request #2184 from yui-knk/fix-typo

Fix typo.
Merge pull request #2185 from suzukaze/hash-comments

Add Hash comments
Merge pull request #2161 from nobu/embedded_document

Embedded document
Add Hash#flatten
Merge pull request #2186 from suzukaze/add-hash.flatten

Add Hash#flatten
Add document of header searcher of compiler.
Merge pull request #2187 from take-cheeze/header_searcher_doc

Add document of header searcher of compiler.
Don't reset ridx,eidx. And fix for #1949
Merge pull request #2188 from takeru/dont_reset_ridx_eidx

Don't reset ridx,eidx. And fix for #1949
add Mrbtest::FIXNUM_{MAX,MIN,BIT}
test fixnum overflow for add, sub and mul
Refactoring exception test.

Change to use assert_equal explicitly.
Merge pull request #2191 from yui-knk/refactor-exc-test

Refactoring exception test.
fix memcpy-param-overlap
Add Hash#invert
Refactor mrb_str_capitalize_bang()