This commit dismisses the `argparse` library (the only non-runtime C
component of rev.ng) in favor of LLVM's CommandLine library, which
offers several benefits. Among others, now command line arguments can be
easily specified as a global variable, decentralizing their management
and avoiding the long list of arguments in the constructor of singleton
objects such as `CodeGenerator`.

The symbol handling has been extended to register whether a symbol
represents a function or not. This information is then used to register,
during the global data harvesting phase, all the function symbols and
explicitly mark them through the "FunctionSymbol" `JTReason`.

We use this information during the CFEP harvesting phase to integrate
the information produced by the function boundaries detection with
potential unidentified CFEPs.

This option can be enabled with the `--use-debug-symbols`, which
supersedes `--use-sections`.

This commit makes `revamb` produce a new file `.ll.need.csv` containing
a list of all the dynamic libraries required by the input program. This
will be transformed by the 'csv-to-ld-options` (was:
`li-csv-to-ld-options`) into the appropriate linking options.

This commit introduces the Function Isolation Pass. We use the
information provided by the Function Boundaries Detection Pass to
organize the code that `revamb` places inside the `root` function in
different LLVM functions. To do this we obviously need to introduce some
changes and tricks to handle the execution of the translated program.

The main idea is to have two different realms (one where the isolated
functions live, one in which we have basically the old root function).
We start the execution from the realm of the *non isolated* functions,
and we transfer, as soon as possible, the execution to the *isolated
functions* realm. We then have a fallback mechanism to restore the
execution in the right place in the *non isolated* functions realm, and
so on.

The largest change, besides the re-organization of the code in different
functions, is the use of the exception handling mechanism provided by
the LLVM framework in order to be able to manage the switch between the
two realms.

We also introduce the `support.h` header file, which contains a couple
of definitions used by `support.c` and that need to be shared with some
of the components involved in the translation process. We have defined
some helper functions, directly in C, that we use both for handling the
exception mechanism and for giving extra debug informations when an
exception is raised.

The `revamb-dump` utility now supports the `-i` option to specify the
path were to save the new LLVM module.

The `translate` utility now supports the `-i` option that produces a
binary in which the function isolation has been applied.

We also introduced some tests that apply the function isolation pass to
the `Runtime/` tests already present. In this way we can verify that the
translation and the following function isolation preserve the behavior
of the program.

When serializing the new LLVM module we regenerate the metadata used for
debug purposes, and for doing this, since we not longer have only the
`root` function, we have changed some details in the `DebugHelper` class
in order to be able to emit the metadata for all the functions of our
interest in a single shot.

This simple commit should improve performance of the generated program
sensibly. Basically all the global variables will have internal linkage
from now on (unless the `--external` parameter is specified on the
command line). This way, the compiler will be able to avoid load/store
instructions when leaving code in the current translation unit.

Introduce the `-disable-machine-licm` argument when the `translate`
script invokes `llc` with `-O2`.

This commit introduces a docs target which translates `.rst` files into
man pages or HTML documents and installs them in `/usr/share/man/man1`
or `/usr/share/doc/revamb`.

Update `GeneratedIRReference.rst:` to reflect recent changes to the
`root` function. Specifically, the presence of the stack pointer
argument and initialization of the program counter and the stack
pointer.

`FromIRToExecutable.rst` has been updated too, to take into account the
new way we link `support.c`.

Finally, the `--tracing` argument has been removed from
`RevambUsage.rst` and the `-trace` argument is no documented in
`TranslateUsage.rst`.