'#+' and '#-' introduce conditional compilation: the form that follows
is kept only when the feature expression is true, and otherwise is read
and thrown away. An expression is a feature name, or and / or / not
of them.
They are read time, not compile time.
Default features are the host's software-version, software-type and
machine-type as CHICKEN reports them, plus what --features flag adds.
compile-to-file returned process-wait's values and main dropped them,
so cc errors were printed, but then main compiler exited 0.
Also cleanup tmp C files when compilation failed.
For source-level debug. Add --line-directives option, defaulted to
statement. Disabled when used with -C. Explicit non-none value
overrides disabling when -C is present
Also rename macros to sex-macros, module-system to sex-modules for
clarity, uniformity, and to avoid name clashes with Chicken's
units/modules named "macros" and "modules"
Introducing Sex SEMantic ENgine: the semen.
Also split reader to other file (it can be replaced in the future).
Macro expansion inside Sex code doesn't work yet, and it must be done
in semen, not during fmt-c generation as before.
Also rework options printing, add some cmdline options, rework others,
all in all, the logic is now looking like this:
* -E to emit C code
* -m to emit macro-expanded Sex code
* -c to emit object file instead of executable
* --c-compiler to set C compiler. If not provided, check SEX_CC
enviroment variable, if it's empty, default to `cc'
* options after -- are passed to C compiler
* default mode is to compile Sex module to executable
