[pdal] Pipeline schema, Options

[Michael P. Gerlek]

Well, that was fun.

(1) The HEAD now follows gadomski's pipeline schema -- your old .xml files
will not work, nope, no way, no siree.

(2) The Options system's implementation has also changed, so that it is no
longer templated and no longer as fragile as it was.  (It is also no longer
backed explicitly by a ptree.)  The protocol for getting/setting options is
simply this:

  - You can set with either a std::string or some other type T.

  - You must specify the template type when you do the get(), i.e.
"getValue<boost::uint32_t>()".  The type of that get<> must be either a
std::string or that same type T you did the set() with.

  - All conversions are done via boost::lexical_cast, so if you are storing
a nontrivial type T, then T must support a copy ctor, oper=, oper<<, and
oper>>.  (Bounds<> does this, for example.)

  - Eschew the use of int8/uint8 types for options, as they look like chars.

-mpg