[split] Move composer plugin to oh-my-fish/plugin-composer

https://github.com/oh-my-fish/plugin-composer

plugins/composer/composer.fish

-# composer command
-function composer
-  if test -e ./composer.phar # if there is composer in this path use local one
-    ./composer.phar $argv;
-  else if test -n "$COMPOSER_BIN"
-    eval "$COMPOSER_BIN" $argv;
-  else
-    echo "Please install composer.phar to your PATH. Or use \"composer_install\" to install Composer to current directory."
-  end
-end

plugins/composer/composer.load

-# add Composer's global binaries to PATH
-if test -z "$COMPOSER_BIN_PATH"
-  set -gx COMPOSER_BIN_PATH $HOME/.composer/vendor/bin
-end
-set PATH $COMPOSER_BIN_PATH $PATH
-
-# get composer path
-if test -z "$COMPOSER_BIN"
-  if type "composer.phar" > /dev/null
-    set -gx COMPOSER_BIN (which composer.phar)
-  else if type "composer" > /dev/null
-    set -gx COMPOSER_BIN (which composer)
-  else
-    echo "FAILED to find Composer! Please install composer.phar to your PATH."
-  end
-end

plugins/composer/composer_install.fish

-# install composer in the current directory
-function composer_install
-  curl -s https://getcomposer.org/installer | php
-end