package debian: add missing "[ ... ]"
Initialize ctx->impl in grn_ctx_init()

Remove lazy ctx->impl initialization feature because it's not useful for
now.
Remove a needless empty line
mrb: bind grn_db
mrb: bind grn_obj_close()
mrb: bind grn_db_open() and grn_db_create()
mrb: use mruby-io
Add grndb command

It does nothing for now. It will implement --check option and --recover
option.
mrb: bind grn_db_recover()
Fix a bug that drilldown value can't be got by _key on command_version=2

We always used code multi-keys drilldown for single key drilldown case
on command_version=2. The problem isn't occurred on command_version=1.

command_version=1 is the current stable version. command_version=2 is
the current development version.

GitHub: fix ranguba/rroonga#38

Reported by YUKI "Piro" Hiroshi. Thanks!!!
package debian: enable armhf platform
package debian: add missing license about parse.c
package debian: describe license about mruby/* files
package debian: add missing armhf as supported architecture
groonga http: support HEAD
mrb: fix indent
mrb: use LoadError for load error
mrb: raise error on load
mrb: export system Ruby scripts directory
mrb: implement require