Get rid of the dependency on "make" to install "bpkg"

Rename install.sh to setup.sh in order to take the Makefile targets.
Former make target names are now passed to the script like

$ ./setup.sh uninstall

Fixes #45.

Makefile

@@ -1,24 +0,0 @@
-# bpkg Makefile
-
-BIN    ?= bpkg
-PREFIX ?= /usr/local
-
-# All 'bpkg' supported commands
-CMDS = json install package term suggest init utils update list show
-
-install: uninstall
-	@echo "  info: Installing $(PREFIX)/bin/$(BIN)..."
-	@install $(BIN) $(PREFIX)/bin
-	@for cmd in $(CMDS); do cp $(BIN)-$${cmd} $(PREFIX)/bin; done
-
-uninstall:
-	@echo "  info: Uninstalling $(PREFIX)/bin/$(BIN)..."
-	@rm -f $(PREFIX)/bin/$(BIN)
-	@for cmd in $(CMDS); do rm -f $(PREFIX)/bin/$(BIN)-$${cmd}; done
-
-link: uninstall
-	@ln -s $(BIN) $(PREFIX)/bin/$(BIN)
-	@for cmd in $(CMDS); do ln -s $(BIN)-$${cmd} $(PREFIX)/bin; done
-
-unlink: uninstall
-

README.md

@@ -35,12 +35,12 @@ $ clib install bpkg/bpkg
 
 ### 3. Source Code
 
-To directly install `bpkg` from it's source code you have to clone it's repository and install with `make`:
+To directly install `bpkg` from it's source code you have to clone it's repository and run the `install` script:
 
 ```sh
 $ git clone https://github.com/bpkg/bpkg.git
 $ cd bpkg
-$ make install
+$ ./setup.sh
 ```
 
 Or in a directory with user write permission, like `$HOME/opt/bin`
@@ -48,7 +48,7 @@ Or in a directory with user write permission, like `$HOME/opt/bin`
 ```sh
 $ git clone https://github.com/bpkg/bpkg.git
 $ cd bpkg
-$ PREFIX=$HOME/opt make install
+$ PREFIX=$HOME/opt ./setup.sh
 ```
 
 ## Usage

setup.sh

@@ -52,13 +52,51 @@ setup () {
     cd "${DEST}"
     echo "  info: Installing..."
     echo
-    make install
+    make_install
     echo "  info: Done!"
   } >&2
   return $?
 }
 
+## make targets
+BIN="bpkg"
+[ -z "$PREFIX" ] && PREFIX="/usr/local"
+
+# All 'bpkg' supported commands
+CMDS="json install package term suggest init utils update list show"
+
+make_install () {
+  make_uninstall
+  echo "  info: Installing $PREFIX/bin/$BIN..."
+  install "$BIN" "$PREFIX/bin"
+  for cmd in $CMDS; do
+    install "$BIN-$cmd" "$PREFIX/bin"
+  done
+  return $?
+}
+
+make_uninstall () {
+  echo "  info: Uninstalling $PREFIX/bin/$BIN..."
+  rm -f "$PREFIX/bin/$BIN"
+  for cmd in $CMDS; do
+    rm -f "$PREFIX/bin/$BIN-$cmd"
+  done
+  return $?
+}
+
+make_link () {
+  make_uninstall
+  ln -s "$BIN" "$PREFIX/bin/$BIN"
+  for cmd in $CMDS; do
+    ln -s "$BIN-$cmd" "$PREFIX/bin"
+  done
+  return $?
+}
+
+make_unlink () {
+  make_uninstall
+}
+
 ## go
-setup
+[ $# -eq 0 ] && setup || make_$1
 exit $?
-