in CMake READLINEDIR is not well enforced

[alaingdl]

We do have to cleanup/improve the way readline is included in GDL.

The problem happens with the current Git version, on OSX & Linux.
I suspect it is just a small problem in the files related to CMake

I did compile locally a Readline from TGZ (configure -prefix=$PWD/Compilation & make & make install)

If I put cmake .. -DQHULL=off -DREADLINEDIR=/home/alain/GDL/Readline8.3/readline-8.3/Compilation
at the end the link is with the "official" one, not the local one :

ldd src/gdl  | grep readl
	libreadline.so.8 => /lib/x86_64-linux-gnu/libreadline.so.8 (0x0000738ab5d0a000)

This is quite important because we do have a problem on OSX with the current Readline coming with Brew.

[alaingdl]

Few information :

• I found a simple way to change FindReadline.cmake to solve the issue with lib path (tested on Linux + OSX) (this problem is specific to Readline due to the readline/readline.h include file. No problem with GSL or FFTw ...)
• Readline 8.3 is problematic for current GDL on OSX 15.5 (intel and arm64 procs.) (GDL is frozen at startup)
• Brew comes with Readline 8.2.13

(I have to collect few other small tips before making a PR)

CMakeModules$ diff FindReadline.cmake_REF FindReadline.cmake
15c15,17
< find_path(READLINE_INCLUDE_DIR NAMES readline/readline.h)
---
> find_path(READLINE_INCLUDE_DIR
>   NAMES readline/readline.h
>   HINTS ${READLINE_LIBRARY})