Move src/*.{c,h} to src/core/

This way we have all libosmocore.so in an own subdir instead of having
lots of files in the parent dir, which also contains subdirs to other
libraries.
This also matches the schema under include/osmocom/.

Change-Id: I6c76fafebdd5e961aed88bbecd2c16bc69d580e2
diff --git a/Doxyfile.core.in b/Doxyfile.core.in
index c2bfcd5..29507e0 100644
--- a/Doxyfile.core.in
+++ b/Doxyfile.core.in
@@ -610,7 +610,7 @@
 # directories like "/usr/src/myproject". Separate the files or directories
 # with spaces.
 
-INPUT                  = @srcdir@/include/osmocom/core @srcdir@/src
+INPUT                  = @srcdir@/include/osmocom/core @srcdir@/src/core
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding, which is