add API routines to create memory dumps

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on October 24, 2013 10:33:05_

A common scenario for a client is to take a snapshot of memory. DR already
has built-in support for its own dump format, the "ldmp". We may want to
expose creation of an ldmp to clients.

We would want to solve the outstanding ldmp limitations (with the viewing
tool, not creation): issue #118 , issue #397 Xref issue #1301 where we may want to also support creating the standard
.dmp format.

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1302_