fix length check in read_section_debug()

Changed a variable declaration to top of block

Change supress to suppress

nextc(): always return an '\n' at end of input

fix #1564

removing irep array from mrb_state.  note that instructions OP_LAMBDA,
OP_EXEC and OP_EPUSH are incompatible, and dumped mrb format has changed.

mrbc: add line break for -c option, like other options

currently there are two scnenario to call mrb_run(), the first is
calling a proc, in this case mrb should create a new environment,
discarding all the variables except args, reciever and block.

the second is calling the newly generated irep, like in mirb.
in this case, the variables should be kept after mrb_run().
so we introduce mrb_context_run() to handle this seperately.