use `extend` for object merging, Fix https://github.com/spmjs/spm/issues/948
support spm_modules, and fallback to sea-modules if spm_modules is not found
Merge pull request #66 from spmjs/spm_modules

support spm_modules, and fallback to sea-modules if spm_modules is not f...
code style
statusCode 404 at 404 page, fix #65
Merge branch 'master' of github.com:spmjs/spmjs.io
Merge pull request #20 from spmjs/master

merge spmjs.io:master