A directory-category for terminal emulators

This is a mostly cosmetical commit, in the sense it doesn't change the contents
of any package, but reorganizes the overall Nixpkgs expressions.

Terminal emulators are an ubiquitous tool for any Unix user; even the beginners
are routinely familiarized to it. And, manifestly, there are many
implementations of terminal emulators out there, from those traditionally made
in C and C++ to those written in Haskell and Go.

Terminal emulators deserve more highlight. This commit does that by creating a
category for them.

pkgs/applications/terminal-emulators/termite/remove_ldflags_macos.patch

@@ -0,0 +1,25 @@
+From 1b5a6934635c55472eb7949bd87ab3f45fa1b2f3 Mon Sep 17 00:00:00 2001
+From: Michael Hoang <enzime@users.noreply.github.com>
+Date: Fri, 13 Jul 2018 19:01:51 +1000
+Subject: [PATCH] Remove --as-needed flag from ld to fix compilation on macOS.
+
+---
+ Makefile | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/Makefile b/Makefile
+index b115f42..ab301ba 100644
+--- a/Makefile
++++ b/Makefile
+@@ -29,7 +29,7 @@ ifeq (${CXX}, clang++)
+ 	CXXFLAGS += -Wimplicit-fallthrough
+ endif
+ 
+-LDFLAGS := -s -Wl,--as-needed ${LDFLAGS}
++LDFLAGS := -s -Wl ${LDFLAGS}
+ LDLIBS := ${shell pkg-config --libs ${GTK} ${VTE}}
+ 
+ termite: termite.cc url_regex.hh util/clamp.hh util/maybe.hh util/memory.hh
+-- 
+2.17.1
+