This also templatizes the Buffer::*Slice functions, and the template
function probably cannot be safely used outside of Node.  However, it
also SHOULD not be used outside of Node, so this is arguably a feature
as well as a caveat.

Move the implementation to C++ land. This is similar to commit 3f65916
but this time for the write() function and the Buffer(s, 'hex')
constructor.

Speeds up the benchmark below about 24x (2.6s vs 1:02m).

  var s = 'f';
  for (var i = 0; i < 26; ++i) s += s;  // 64 MB
  Buffer(s, 'hex');

Move the implementation to C++ land. The old JS implementation used
string concatenation, was dog slow and consumed copious amounts of
memory for large buffers. Example:

  var buf = Buffer(0x1000000);  // 16 MB
  buf.toString('hex')           // Used 3+ GB of memory.

The new implementation operates in O(n) time and space.

Fixes #4700.

Improvements:
* floating point operations are approx 4x's faster
* Now write quiet NaN's
* all read/write on floating point now done in C, so no more need for
  lib/buffer_ieee754.js
* float values have more accurate min/max value checks
* add additional benchmarks for buffers read/write
* created benchmark/_bench_timer.js which is a simple library that
  can be included into any benchmark and provides an intelligent tracker
  for sync and async tests
* add benchmarks for DataView set methods
* add checks and tests to make sure offset is greater than 0

Use static_cast instead of reinterpret_cast when casting from void*
to another type.

This is mostly an aesthetic change but may help catch bugs when the
affected code is modified.

Also Revert "buffer: use MAP_ANON, fix OS X build"

This reverts commit ddb15603e74e9aa865f3e1099dc2cc5886f9c46e.
This reverts commit 2433ec8276838e90136669d5b1215ba597f15fdd.

Work around an issue with the glibc malloc() implementation where memory blocks
are never returned to the operating system when they are allocated with brk()
and have overlapping lifecycles.

Fixes #4283.

Change Buffer::New(char*, size_t) to Buffer::New(const char*, size_t).

Make Buffer:Data() and Buffer::Length() accept a Value instead of an Object.