Remove unnecessary variable and else-if #cosmetic

Recommend --word-diff-regex='\w+|.' to view diff.

I first noticed that we were doing isObject() twice if an object is
passed as `def` in the first place, and in simplifying that I realized
we didn't even need `extensions` in the first place.

`for (var ext in def)` didn't make much sense so I changed the name of
the iteration variable too.
Inline `isObject` #cosmetic

Recommend --word-diff (default regex, not '\w+|.'), and GIT_PAGER= so
that the line in the README won't word-wrap, e.g.:
```sh
$ GIT_PAGER= git show --word-diff
```
use `Bare` in the idiomatic subclassing test
Merge pull request #24 from laughinghan/master

Cosmetic fixes: delete outdated comment, fix typo
Merge pull request #21 from laughinghan/refactor.cosmetic

Simplify and reduce minified size without reducing functionality
just require package.json, no need for JSON.parse
Don't fail silently if .init isn't a function #cuttingFeatures

Because of the check for inheriting a non-pjs class, the only way for
that to happen is if you monkey-patch .init to something that isn't a
function, in which case you'll get a

    TypeError: Object ${thing you monkey-patched .init to} has no method 'apply'

which I feel like is excellent behavior.

<0.4kb now!

Conflicts:
	README.md
	src/p.js
Simplify check if inheriting from a non-Pjs class

If proto.init is truthy but not a function, like 1 or something, you'll
get a

    TypeError: Object 1 has no method 'apply'

which I feel like is excellent behavior.

If we're inheriting from a Pjs class but `proto.init` is overridden to a
falsy value, we'll think we're inheriting from a non-Pjs class and set
`proto.init` to the superclass constructor, which isn't the most
defensive, fail-early thing to do, but is also what happened prior to
this commit.

Really, to be defensive in our non-pjs check, we should check
`('init' in proto)`, so if `proto.init` is overridden to anything
but a function it'll TypeError like above.
only set the .init property if it's actually missing
Merge branch 'refactor.minify-optimizations'
inline the hasOwnProperty check
be more defensive when setting .init to the superclass

This only sets it when it doesn't exist anywhere on the prototype chain,
rather than when it's set to a falsy value.
Revert "inline the hasOwnProperty check"

This reverts commit c52a23a05422be712c726321417ffbcff2253eca.
kill SuperclassBare in favor of re-using Bare
shave 2 bytes by hoisting `var key` up one closure