Rewrite a shebang line of each bin/* scripts if REWRITE_SHEBANG is set

ExtUtils::MakeMaker rewirtes #/usr/bin/perl or #!perl but NOT
#!/usr/bin/env perl, so mandatorily rewrite shebang if environment variable
REWRITE_SHEBANG is set.

- https://github.com/Perl-Toolchain-Gang/ExtUtils-MakeMaker/issues/58
Merge pull request #12 from hirose31/feature/rewrite-shebang

Rewrite a shebang line of each bin/* scripts if REWRITE_SHEBANG is set