Rename INSTALL_TOP to PREFIX; update documentation

Signed-off-by: Pedro Melo <melo@simplicidade.org>

INSTALL

@@ -3,7 +3,18 @@ To compile Redis, do the following:
     cd src; make
 
 The compilation will produce a redis-server binary.
-Copy this file where you want.
+
+To install Redis, use
+
+    make install
+
+and all the binaries will be installed on /usr/local/bin.
+
+Alternatively:
+
+    make PREFIX=/some/other/directory
+
+to have the binaries in /some/other/directory/bin.
 
 Run the server using the following command line:
 

README

@@ -16,7 +16,8 @@ It is as simple as:
 
 Redis is just a single binary, but if you want to install it you can use
 the "make install" target that will copy the binary in /usr/local/bin
-for default.
+for default. You can also use "make PREFIX=/some/other/directory install"
+if you wish to use a different destination.
 
 You can run a 32 bit Redis binary using:
 

src/Makefile

@@ -15,7 +15,7 @@ endif
 CCOPT= $(CFLAGS) $(CCLINK) $(ARCH) $(PROF)
 DEBUG?= -g -rdynamic -ggdb 
 
-INSTALL_TOP= /usr/local
+PREFIX= /usr/local
 INSTALL_BIN= $(INSTALL_TOP)/bin
 INSTALL= cp -p