It now takes a frame cursor ref instead of a stack ref.

This will give the user more control over logging in Holstein.
Specifically, the XML configuration can configure appenders so that logs
can be written into stderr instead of stdout.

Switched Scala version to 2.12.2, the most recent stable version.  It
will now require Java 1.8.

Fixed existing uses of deprecated features.

Removed the `uvm.clientsupport` package.  This package was intended to
help Mu clients build text-based Mu IR bundles.  However, we started
using the IR Builder API instead, and the `uvm.clientsupport` package
remained unused.  The same capability can be provided by the
`mu-tool-compiler` project
(https://gitlab.anu.edu.au/mu/mu-tool-compiler).  `uvm.clientsupport`
provided a non-SSA-to-ssa converter, which can be useful for clients.
If there are needs of resurrecting that feature, please checkout the
previous commit.

Now it no longer assume the higher 16 bits of a ref are either all 0s or
all 1s.  The layout of bits of tabref64 is changed, but is not visible
to the client.

Type inferer and predefined entities are no longer single objects.  They
can be instantiated like other classes.

An SSA variable now has an `inferred type` field which represents its
type.  The type is filled in when loading a bundle, and can be dependedn
on during execution.

Added stricter static checking related to variable types.

Fixed some problem left in the operations for tagref64 which are caused
by porting from microvm-p2, the legacy Python-based Micro VM
implementation.

Added documentation and test cases for tagref64-related operations.

This will allow mu-client-pypy to use this hack in the master branch by
setting the --uPtrHack=true VM option.

It should treat the string parameter as an iref to a 0-terminated
string.

- Implemented @uvm.irbuilder.new_ir_builder

- Fixed @uvm.irbuilder.gen_sym where the %name parameter should be optional

Now "automagic relocation" can be enabled by a VMConf option
"automagicReloc".  It is disabled by default.

Manual symbols can be added via the make_boot_image api function.

Note: curently manual symbols can only be used during boot image
building, and can be used for relocations, only.  At run time, the
manual symbols are invisible, because Holstein cannot actually generate
ELF (or MachO) images compatible with native programs.

Moved from the deprecated "flat" sbt project definition style to the
recommended "multi-project" style.

Bumped dependency versions.

This will fix the problem that some memory is reclaimed by the GC before
the intended end-of-life. Now many classes implement the AutoCloseable
interface and manage their resources in the C++ style.

Need testing...

Moved CanBeIntegerized to its own package.

Removed "Word" from TypeSizes and uniformly import from uvm.refimpl.

Lifted xxxEntity outside match.

Fixed a bug in MemorySupport.cmpXchgEntity

TODO: Implement the new IR builder.