Add an option to mandelbrot to make it easier to test parallelism

Add a --parallel command line option to the mandelbrot benchmark that can be
given to use explicitly parallelised routines.  This makes it easier to turn
on and off explicit parallelism, depending on your testing needs.

benchmarks/progs/mandelbrot/mandelbrot.m:
    As above
Do not escape character strings in internal atom representation.

The internal representation of a character constant as an atom term
should not use escaped character syntax; the escaping should occur
when writing the external representation only.

compiler/hlds_out_mode.m:
compiler/intermod.m:
compiler/prog_util.m:
compiler/type_constraints.m:
compiler/typecheck.m:
	Fix instances of the bug.

tests/valid/Mercury.options
tests/valid/Mmakefile
tests/valid/intermod_char.m
tests/valid/intermod_char2.m
	Add test case.  The .opt file was invalid because the character
	in the clause head was doubly-escaped.
Merge fix for bug #330 into version-14_01-branch

Commit 5254245ae34ab6b3ca0f7dcd3c7fc807e1407f7d was inadvertently
merged onto version-14_01-branch but NOT the subsequent fix in
commit 8c72b1e5c0c23353770c494bcdf35a450ebf7c85
Create README.md

(Commit log by Paul Bone)

Github will automatically format and display a file named README.md in the
root directory of any project.  This can be helpful to, at a minimum, direct
anyone browsing github to the project's website.  Sebastian has contributed
the following README.md.

README.md:
    New markdown-formatted README file for github.
README.md changes

README.md:
    Changed intro to www.mercurylang.org introduction.

    Added a NOTES and LIMITATIONS section.

    Added a link to the README.bootstrap.
Make a number of changes to the README.md file

README.md:
    Reorder the list or README files to that they occur from most relevant
    to new users to least relevant.  In particular put commonly-used
    backends and platforms earlier in the list.

    Provide some introductory text that introduce the user to the multiple
    backends available.

    Add further links to more information such as the documentation.

    Add text so that the file reads more natrually.
Fix no_refs_to_deleted_labels failures.

MR_LOWLEVEL_DEBUG is set when compiling the no_refs_to_deleted_labels
test case to give MR_init_label macros some effect.  However
MR_LOWLEVEL_DEBUG implies MR_DEBUG_GOTOS, and leads to link errors if
the runtime was not built with MR_DEBUG_GOTOS.

tests/hard_coded/Mercury.options:
	Replace MR_LOWLEVEL_DEBUG with MR_DEBUG_LABEL_NAMES,
	implying MR_INSERT_LABELS but not MR_DEBUG_GOTOS.
Merge branch 'version-14_01-branch'
Merge branch 'version-14_01-branch'
Edit README.md

README.md:
    Fixed whitespace.

    Made more succinct.
Make Julien's review suggestions

README.md:
    Remove references to lcc (hasn't been tried with Mercury for years)
    and the old .NET backend from README.md (likely to cause confusion
    more than anything else).

README.md:
README.IRIX-5:
    Remove the references to IRIX-5 (including the file README.IRIX-5)
    completely.  IRIX is pretty much dead, this documentation is pretty
    much clutter at this point.

README.AIX:
README.HPUX:
    Replacing the contents of README.HPUX and README.AIX to say that
    Mercury (to the best of our knowledge) hasn't been tried with recent
    versions of those OSs.
Merge branch 'readme'

Merge in the changes that introduce and fxiup the README.md file.