Add support for downloading single blobs

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

Makefile

@@ -9,7 +9,7 @@ CACHE_ROOT = /var/cache/cgit
 EXTLIBS = $(gitsrc)/libgit.a $(gitsrc)/xdiff/lib.a -lz -lcrypto
 OBJECTS = shared.o cache.o parsing.o html.o ui-shared.o ui-repolist.o \
 	ui-summary.o ui-log.o ui-view.o ui-tree.o ui-commit.o ui-diff.o \
-	ui-snapshot.o
+	ui-snapshot.o ui-blob.o
 
 CFLAGS += -Wall