refactor all history modifications into discrete plugins

plugins/available/history-search.plugin.bash

@@ -0,0 +1,9 @@
+cite about-plugin
+about-plugin 'search history using the prefix already entered'
+
+# enter a few characters and press UpArrow/DownArrow
+# to search backwards/forwards through the history
+if [[ ${SHELLOPTS} =~ (vi|emacs) ]]; then
+	bind '"\e[A":history-search-backward'
+	bind '"\e[B":history-search-forward'
+fi

plugins/available/history-substring-search.plugin.bash

@@ -0,0 +1,9 @@
+cite about-plugin
+about-plugin 'search history using the substring already entered'
+
+# enter a few characters and press UpArrow/DownArrow
+# to search backwards/forwards through the history
+if [[ ${SHELLOPTS} =~ (vi|emacs) ]]; then
+	bind '"\e[A":history-substring-search-backward'
+	bind '"\e[B":history-substring-search-forward'
+fi

plugins/available/history.plugin.bash

@@ -1,9 +1,11 @@
 cite about-plugin
-about-plugin 'history manipulation'
-# enter a few characters and press UpArrow/DownArrow
-# to search backwards/forwards through the history
-if [[ ${SHELLOPTS} =~ (vi|emacs) ]]
-then
-    bind '"":history-search-backward'
-    bind '"":history-search-forward'
-fi
+about-plugin 'improve history handling with sane defaults'
+
+# append to bash_history if Terminal.app quits
+shopt -s histappend
+
+# erase duplicates; alternative option: export HISTCONTROL=ignoredups
+export HISTCONTROL=${HISTCONTROL:-ignorespace:erasedups}
+
+# resize history to 100x the default (500)
+export HISTSIZE=${HISTSIZE:-50000}