[dfmc-modeling] Remove method environment(<&method>).

This method wasn't used and returned an empty vector rather than
a valid environment object.
[dfmc-modeling] Tighten types on environment generic & methods.
Remove unmaintained PowerPC OS X materials.
[build] Allow installing on top of an existing install.

Fixes issue #753.
Merge pull request #786 from waywardmonkeys/allow-install-on-top

[build] Allow installing on top of an existing install.
[c-back-end,c-linker] Use $dylan-type-string instead of "D".

This is in preparation for renaming types within the C run-time.
[c-run-time] Rename many struct types to have dylan_* names.

This will improve our debugging support and make many things
more approachable to users who aren't experts in the internals
of the C run-time.

More changes are coming in subsequent commits.
[c-back-end] Capitalize $dylan-type-string in certain function names.

We want the $dylan-type-string to be capitalized when used in
generated function names like MAKE_D_CELL and so on.
[crt,c-back-end] Switch to using "dylan_value" instead of "D" for Dylan values.

A Dylan value is a tagged value and may be an integer, byte character,
unicode character or a dylan_object.

This change is useful for working with lldb as the currently shipping
version of lldb crashes when adding a summary function for 'D'.

The type "D" is maintained for 2 reasons: just in case, for backwards
compatibility and in some situations it is used as the type for a
raw pointer. We will shift that over to "void *" in subsequent
commits.
[crt] D -> dylan_value.
Merge pull request #785 from waywardmonkeys/c-run-time-type-names

C run time type names
Merge pull request #787 from waywardmonkeys/remove-ppc-darwin

Remove unmaintained PowerPC OS X materials.
[doc] Document alternative curry syntax.
[projects] Display warning for invalid base-address.
Merge pull request #788 from waywardmonkeys/document-alternative-curry-syntax

[doc] Document alternative curry syntax.
Merge pull request #789 from fracek/invalid-base-address

[projects] Display warning for invalid base-address.
Remove unused local bindings.
[doc,getting-started-cli] Add note about signal handling when debugging code generated by HARP.
Merge pull request #781 from waywardmonkeys/method-environment

Method environment
Merge pull request #790 from fracek/remove-unused-local-bindings

Remove unused local bindings.