Move header files to subdirectory

Since slweb is meant as a library, it is advisable to keep public header
files under their own directory in order to avoid name clashing i.e.,

 #include "something.h"

Now becomes:

 #include "slweb/something.h"

1 files changed, 1 insertions, 1 deletions

diff --git a/html.c b/html.c
index 41ce387..f916ec0 100644
--- a/html.c
+++ b/html.c
@@ -1,6 +1,6 @@
 #define _POSIX_C_SOURCE 200809L
 
-#include "html.h"
+#include "slweb/html.h"
 #include <dynstr.h>
 #include <errno.h>
 #include <stddef.h>