set handler for mruby_init and mruby_init_code
reorder directives

bring directives of except handlers to head.
call required handlers

== previous ==

All handlers are allways called except following direcitives'

 * mruby_init
 * mruby_init_code
 * mruby_header_filter
 * mruby_header_filter_code
 * mruby_body_filter
 * mruby_body_filter_code

And all file and inline handler's directives are enabled
for multi-definition in same context except following directives.

 * mruby_init
 * mruby_init_code

== current ==

Only defined directives in nginx.conf are called.
And all file and inline handler's direcitives are disabled
for multi-definition in same context except following directives.

 * mruby_set
 * mruby_set_code
remove discarded code
fix bug(ctx->table is collected as garbage by mruby's gc)

mrb_gc_protect is required in this case.
remove (post_read|server_rewrite)_handler

These handlers are not required in HTTP
add header files to NGX_ADDON_DEPS
fix up style
forgot to initialize context in mruby_set
context never become NULL in ngx_mrb_run
clear spaces
fix bug(return incorrect result value in filters)
bumped version to 0.1.0