* Change calls to String::New() and String::NewSymbol() to their
  respective one-byte, two-byte and UTF-8 counterparts.

* Add a FIXED_ONE_BYTE_STRING macro that takes a string literal and
  turns it into a v8::Local<v8::String>.

* Add helper functions that make v8::String::NewFromOneByte() easier to
  work with. Said function expects a `const uint8_t*` but almost every
  call site deals with `const char*` or `const unsigned char*`. Helps
  us avoid doing reinterpret_casts all over the place.

* Code that handles file system paths keeps using UTF-8 for backwards
  compatibility reasons. At least now the use of UTF-8 is explicit.

* Remove v8::String::NewSymbol() entirely. Almost all call sites were
  effectively minor de-optimizations. If you create a string only once,
  there is no point in making it a symbol. If you are create the same
  string repeatedly, it should probably be cached in a persistent
  handle.

Commit 847c6d9 adds a 'project headers before system headers' check
to cpplint. Update the files in src/ to make the linter pass again.

V8 3.20.9 enforces that external pointers are aligned on a two-byte
boundary.

We cannot portably guarantee that for the source code strings that
tools/js2c.py generates so simply stop using String::NewExternal()
altogether (and by extension String::ExternalAsciiStringResource).

Fixes the following run-time assert:

  FATAL ERROR: v8::String::NewExternal() Pointer is not aligned

Update the api to pass node_isolate to all supported methods.

Much thanks to Ben Noordhuis and his work in 51f6e6a.

Change the natives to use this class instead of creating completely new
strings. Reduces memory usage by about 1 MB.