gnu: Add ghc-mtl-compat.

* gnu/packages/haskell-xyz.scm (ghc-mtl-compat): New variable.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu: Add ghc-sourcemap.

gnu/pacakges/haskell-web.scm (ghc-sourcemap): New variable.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu: Add ghc-wai-websockets.

* gnu/packages/haskell-web.scm (ghc-wai-websockets): New variable.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu: Add ghc-websockets.

* gnu/packages/haskell-web.scm (ghc-websockets): New variable.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu: Add ghc-tasty-hspec.

* gnu/packages/haskell-check.scm (ghc-tasty-hspec): New variable.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu: Add ghc-transformers.

* gnu/packages/haskell-xyz.scm (ghc-transformers): New variable.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu: Add ghc-utf8-light.

* gnu/packages/haskell-xyz.scm (ghc-utf8-light): New variable.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu: rtl-sdr: Fix location of udev rules file.

* gnu/packages/radio.scm (rtl-sdr)[arguments]: Modify 'fix-paths' phase to put
  the udev rules file in 'lib/' instead of 'etc/'.

gnu: powertop: Fix typo in description.

* gnu/packages/linux.scm (powertop)[description]: Excise space.

gnu: acpi-call-linux-module: Update to 3.17-0.70b9c80.

* gnu/packages/linux.scm (acpi-call-linux-module): Update to
3.17-0.70b9c80.
[arguments]: Remove ‘fix-for-linux-4.12’ phase.

gnu: powertop: Update to 2.12.

* gnu/packages/linux.scm (powertop): Update to 2.12.

pack: Factorize 'exec_in_user_namespace' wrapper.

* gnu/packages/aux-files/run-in-namespace.c (exec_in_user_namespace):
New function, with code taken from...
(main): ... here.  Call it.

pack: Add 'xmalloc' in wrapper.

* gnu/packages/aux-files/run-in-namespace.c (xmalloc): New function.
(concat): Use it.

pack: Fix off-by-one in PRoot handling in the wrapper.

* gnu/packages/aux-files/run-in-namespace.c (exec_with_proot): Make
'proot_argv' one element larger to account for the terminating NULL.

gnu: Add emacs-tramp.

* gnu/packages/emacs-xyz.scm (emacs-tramp): New variable.

gnu: rtl-sdr: Install udev rules.

* gnu/packages/radio.scm (rtl-sdr)[arguments]: Add '-DINSTALL_UDEV_RULES=ON'
  to configure-flags and add a 'fix-paths' phase to put the udev rules in the
  right place.
  [description]: Indicate how to add the udev rules to the system
  configuration.

gnu: Add icedove.

* gnu/packages/gnuzilla.scm (%icedove-build-id, icedove): New variables.

Co-authored-by: Nikita <nikita@n0.is>
Co-authored-by: Adrian Malacoda <malacoda@monarch-pass.net>
Co-authored-by: Ricardo Wurmus <rekado@elephly.net>

gnu: mu: Remove dubious TODO.

We don't actually want to add mug, ‘just a toy which is not meant for
distribution.’ (NEWS.org)

* gnu/packages/mail.scm (mu): Remove a comment encouraging it.

gnu: mu: Update to 1.4.4.

* gnu/packages/mail.scm (mu): Update to 1.4.4.
[source]: Update URI.

doc: Use @option for command-line options

* doc/guix.texi (Invoking guix system): Use @option instead of @code.