fix Vector#normalize
Merge pull request #21 from meganemura/fix-vector-normalize

fix Vector#normalize
simplified vector operations & their docs
Vector#magnitude as alias for #length
Vector#unit as alias for #normalize
CHANGELOG is now a markdown file
removed redundant rake in Gemfile
updated gemspec
0.3.4
API reference 0.3.3 -> 0.3.4 in README
Allow specifying custom directory for new project

Before you could specify custom directory for the project, but the
template would still be copied to `game`, which might be confusing.
yeah new: name optional, updated usage docs
Merge branch 'new-cmd'