fix(ebuild/eapi): make sure to export vars used in bash

It appears we weren't exporting all the variables that the bash code
references in different places.
feature(eapi-bash): support generic command deprecation for EAPIs

This works similarly to the already existing banned command support.
Briefly explained, within the helpers directory a symlink is created
inside the related EAPI directory that points to the
internals/deprecated script and is named for the deprecated command.
This script then overrides the real command and when called during the
processing of an ebuild with a matching EAPI echoes a QA warning before
executing the intended command.
fix(eapi-bash): make colored messages work as expected

Colors were being disabled on import of isolated-functions.lib file (I'm
not sure why) and variables relating to color escape codes weren't being
exported so things like eqawarn messages weren't getting colored
properly in certain cases, e.g. when run via deprecated commands such as
dohtml in EAPI 6.
feature(eapi-bash): add a general method for deprecating or banning fcns

This allows us to specify function names in BANNED_FUNCS or
DEPRECATED_FUNCS variables in the related EAPI file to easily show QA
warnings for deprecated functions or error messages for banned
functions. The alternative would be explicitly defining function
overrides for every function in the related EAPI file which is verbose
and annoying.
fix(eapi-bash): make INTERNAL_FUNCS local so it doesn't get exported
feature(eapi6): initial EAPI 6 profile and function stubs

We should figure out a way to dynamically build a list of export blocks
for EAPI dependent functions, i.e. we shouldn't block exports from
eclasses for similarly named functions but instead override them with
internal PM implementations when EAPI provided functionality comes into
existence.

The current method involves explicitly adding the related functions to
the INTERNAL_FUNCS list the only current affected function being "usex"
that is defined in EAPI 5 and in the eutils.eclass for EAPI < 5. This
requires us to track implementations within eclasses which can be
problematic.
feature(eapi6): initial get_libdir implementation

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=463586
feature(eapi6): add .txz unpacking support

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=458102
feature(eapi6): initial PATCHES support in src_prepare

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=463692
feature(eapi6): initial eapply_user implementation

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=475288
feature(eapi6): mark dohtml as deprecated (not part of spec?)
feature(eapi6): add support for econf/einstall --docdir and --htmldir (todo)

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=468202
feature(eapi6): initial einstalldocs implementation

HTML_DOCS support might be tacked on later if that becomes part of the
spec.

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=459692
feature(eapi6): add directory support for DOCS

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=481980
feature(eapi6): add support for explicitly disabling DOCS install

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=463736
feature(eapi6): add global failglob setting support (todo)

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=463822
feature(eapi6): ban einstall

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=524112
feature(eapi6): initial nonfatal die support

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=451938
feature(eapi6): initial unpack() absolute path support settings (todo)

X-Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=483244