Sort out the variables which belongs to 'mrb_callinfo' to improve 'cipush' performance.
Merge pull request #2080 from crimsonwoods/replace_disordered_callinfo_variables

Sort out the variables which belongs to 'mrb_callinfo'
Allow parenthesed do-block in cmdarg

Flush cmdarg flags inside left-paren in a command argument, to allow
parenthesed `do-block` as an argument without arguments parentheses.
`CMDARG_PUSH(0)` for tLPAREN_ARG is before `CMDARG_PUSH(1)` in
`command_args` due to look-ahead.
Merge pull request #2081 from nobu/parenthesed_do-block_in_cmdarg

Allow parenthesed do-block in cmdarg
Use boolean macro instead of integer literal in `is_debug_info_defined`.
Merge pull request #2083 from take-cheeze/use_bool_macro

Use boolean macro instead of integer literal in `is_debug_info_defined`.
Fix typos in tests for mruby-string-utf8
Add Rake command 'deep_clean' which cleans everything including the mrbgems clone directories.
Implement :checksum_hash mrbgem option.

This allows to use a mgem with a specific checksum hash.
The following modification were necessary to implement this
function:
  - add run_checkout build command to use 'git checkout'
  - skip shallow copy in case checksum_hash is used
  - make 'master' the default branch if branch isn't defined
Symbol class include Comparable module.
String#casecmp should be call `to_str`
when non String object sent
And should be raise TypeError
when can not responsed to `to_str`
Implement Symbol#casecmp
Add AUTHORS "Yuki Kurihara"
Merge pull request #2084 from suzukaze/fix-typo

Fix typos in tests for mruby-string-utf8
Merge pull request #2090 from ksss/authors

Can I add me to AUTHORS?
Merge pull request #2085 from bovi/deep_clean

Add Rake command 'deep_clean' which cleans everything including the mrbg...
Merge pull request #2086 from bovi/checksum_hash

Implement :checksum_hash mrbgem option
Merge pull request #2087 from ksss/sym-comparable

Symbol class include Comparable module.
Merge pull request #2088 from ksss/string-casecmp

String#casecmp should be call `to_str`
Merge pull request #2089 from ksss/sym-casecmp

Implement Symbol#casecmp