Rearrange allocator headers

This moves the allocator headers from 'container' to a new
top-level 'allocator' directory.

Also renames allocator<T> to buffer_allocator<T>.
Merge pull request #257 from kylelutz/rearrange-allocators

Rearrange allocator headers
Fix '-Wreorder' warning in nbody example

This fixes the following warning in the nbody example: "warning:
field 'm_dt' will be initialized after base 'QGLWidget'"
Merge pull request #258 from kylelutz/fix-nbody-warning

Fix '-Wreorder' warning in nbody example
Add address_space enum to memory_object
Use address_space enum for meta_kernel::add_arg()
Merge pull request #243 from kylelutz/address-space-enum

Address space enum
Fix bug when using popcount() with ulong
Merge pull request #260 from kylelutz/fix-popcount-with-ulong

Fix bug when using popcount() with ulong
Add dynamic_bitset class
Merge pull request #259 from kylelutz/dynamic-bitset

Add dynamic_bitset class