directory re-organization (keeps the old build system)

there is no internal modification of any file in this commit

files are moved into directories according to established standards in
sourcecode distribution; these directories contain:

 src - Files that are used in constructing the executable binaries,
       but are not installed.

 doc - Files in HTML and text format that document usage, quirks of
       the implementation, and contributor checklists.

 locale - Files that contain human language translation of strings
          used in the program

 contrib - Files contributed from distributions or other third party
 	   implementing scripts and auxiliary programs

.gitignore

@@ -1,3 +1,3 @@
-*.exe
-bitcoin
-bitcoind
+src/*.exe
+src/bitcoin
+src/bitcoind