assembler: Separate implementations into different files

Makes the instruction implementations a little more organized without
cluttering up assembler.cpp too much.

Chiefly we just want to split up the compressed instructions and the
scalar floating-point instructions, since they're quite numberous
and also very likely to be open to more expansion in the future.

src/CMakeLists.txt

@@ -3,12 +3,15 @@
 add_library(biscuit
     # Source files
     assembler.cpp
+    assembler_compressed.cpp
     assembler_crypto.cpp
+    assembler_floating_point.cpp
     assembler_vector.cpp
     code_buffer.cpp
     cpuinfo.cpp
 
     # Headers
+    assembler_util.hpp
     "${PROJECT_SOURCE_DIR}/include/biscuit/assembler.hpp"
     "${PROJECT_SOURCE_DIR}/include/biscuit/assert.hpp"
     "${PROJECT_SOURCE_DIR}/include/biscuit/code_buffer.hpp"