Shared objects are built on top of `tao_shared_data_t` instances which
provide a mechanism for r/w locking the resource.  The code for
finalizing shared resources is simpler because we can assume that
the mutex associated to shared data is always owned for a short period.
This will also simplifies getting images from a remote camera: semaphores
will no longer be needed (code compiles but is broken for now in that
respect).

Most functions return a `tao_status_t` to represent success, error or
timeout.  This simplifies and unifies calls to functions with a duration
limit.  This makes the code more clear about the intention:
`foo(...) == TAO_OK` is much better than `foo(...) == 0` or, worse,
`!foo(...)`.

Code for C libraries is now in directories:
  libs/src/core    - core TAO libraries (libtao, libtao-xpa and libtao-fits)
  libs/src/andor   - TAO library for Andor cameras (libtao-andor)
  libs/src/phoenix - TAO library for cameras using Phoenix frame grabber
                     (libtao-phoenix)

Configure script works for the two first components (core and Andor
libraries).

New "Signed" encoding colorant for signed integers so that all
array element types have an equivalent encoding.  "Unsigned" encoding
colorant is an alias for "Monochrome".

New functions `tao_encoding_of_eltype` and `tao_eltype_of_encoding` to
convert between pixel encodings and array element types (when possible).

New functions `tao_name_of_eltype` and `tao_description_of_eltype`.

Header <tao-encodings.h> has been removed (it is now part of <tao.h>).

Some functions have been renamed:

- `tao_get_element_size` -----> `tao_size_of_eltype`
- `tao_encoding_from_name` ---> `tao_parse_encoding`
- `tao_name_of_encoding` -----> `tao_format_encoding`
- `tao_encoding_to_name` -----> `tao_format_encoding`

Enumeration `tao_element_type_t` is now `tao_eltype_t`, constants
`TAO_FLOAT32` and `TAO_FLOAT64` are now `TAO_FLOAT` and `TAO_DOUBLE`.

Header file "macros.h" has been renamed as "common.h" and is meant to be
included *before* other headers.  It should be the only one which includes
"config.h" (so that it is easier to make fixes there).  Since this file
includes "config.h", it is not meant to be installed (unlike "tao.h" or any
other "tao-*.h")

I decided to use the same rule of thumb as in Yorick as (i) `long` integer
type is usually 32 bits on 32-bit machines and 64 bits machines and
(ii) `long` is a signed integer type which is very useful (compared to, e.g.,
`size_t`) to detect errors and to compute offsets.

- In tao_fetch_next_frame and tao_publish_next_frame, it is now assumed
  that the caller (the frame grabber server) has locked the shared camera
  data.

- Some time-stamp functions now return their destination.

- No longer include "config.h" in "tao-private.h" so that "tao-private.h"
  can be included by others.