Add convenience aliases for list types

Add convenience alias for lists of suites
Add convenience alias for lists of tests
Add convenience alias for lists of tasks
Replace aggregate-copy braces with parentheses

GCC, as of 4.8.2, does not support {}-style copy construction of
aggregate types. The value_type of an argument may be aggregate, so it
cannot be initialized using braces.
Replace auto type commitment with explicit typing

GCC, as of 4.8.2, does not support the "auto x = type{}" syntax for
stream types as they do not provide public move or copy constructors.
To maintain consistency, all such initializations have been replaced
with "type x{}" throughout the codebase.
Replace = member-initialization with braces
Add arguments for true and false to evaluator

The true and false statements in the evaluator cannot rely on the
XTF_ARGUMENT macro to create arguments representing true and false,
because XTF_NO_MACROS may have been defined prior to the inclusion of
evaluator.hpp. Instead, the initialization is done manually in static
class variables.
Fix installation of header hierarchy

CMake's PUBLIC_HEADER facilities do not preserve the hierarchy of the
header files given. PUBLIC_HEADER is only necessary for creating Mac
frameworks, which Xtf does not support. Therefore, headers may be
installed using a separate install directive.