RAM optimizations: pseudo RO strings, functions in Flash

This patch adds more RAM optimizations to eLua:

- direct file memory mapping: files in ROMFS will be read directly from Flash,
  without allocating any additional buffers. This doesn't help with RAM
  consumption in itself, but enables the set of optimizations below.

- pseudo read-only strings. These are still TStrings, but the actual string
  content can point directly to Flash. Original Lua strings are kept in
  TStrings structures (lobject.h):

  typedef union TString {
    L_Umaxalign dummy;  /* ensures maximum alignment for strings */
    struct {
      CommonHeader;
      lu_byte reserved;
      unsigned int hash;
      size_t len;
    } tsv;
  } TString;

  The actual string content comes right after the union TString above.
  Pseudo RO strings have the same header, but instead of having the string
  content after TString, they have a pointer that points to the actual
  string content (which should exist in a RO memory (Flash) that is directly
  accesbile from the MCU bus (like its internal Flash memory)). lua_newlstr
  detects automatically if it should create a regular string or a pseudo RO
  string by checking if the string pointer comes from the Flash region of the
  MCU. This optimization works for both precompiled (.lc) files that exist in
  ROMFS and for internal Lua strings (C code).

- functions in Flash: for precompiled (.lc) files that exist in ROMFS, the code
  of the functions and a part of the debug information will be read directly
  from Flash.

- ROMFS was changed to support files that are larger than 2**16 bytes and it
  aligns all its files to an offset which is a multiple of 4 in order to prevent
  data alignment issues with precompiled Lua code.

- the Lua bytecode dumper was changed to align all the instructions in a Lua
  function and a part of the debug information to an offset which is a multiple
  of 4. This might slightly increase the size of the precompiled Lua file.

These changes were succesfully checked against the Lua 5.1 test suite.
These changes were tested in eLua on LM3S and AVR32.
Fixed timer counting direction on all platforms

On some platforms, the hardware timers were counting down instead
of up, which broke the assumptions of the new timer implementation.
Fixed by inverting the timer value (relative to its maximum value).
Fixed the configuration file in order to work with the web builder

Signed-off-by: Nuccio Raciti <raciti.nuccio@gmail.com>
Changed FS registration mechanism

Now it's possible to have more than one instance of a given file
system. For example, one could use more that one ROM file system
in different physical locations (a possible configuration is
internal Flash and external serial memories). This mechanism is
currently implemented only in the device manager (devman.c),
actual instance implementation require per-FS support (to be
implemented later).
Added FS registration data as argument to all FS functions

All the functions that implement a FS receive the instance data
of the FS (given at registration time to dm_register) as their
last argument. ROMFS was changed to take advantage of this.
Changed the ROMFS terminator char

The ROMFS termination char is now 0xFF instead of 0x00 (in preparation
of WOFS).
shell: multiple fixes

1. the filename for 'recv <filename>' was not set correctly
2. error messages for 'cp' were not always correct
3. check for copy errors and issue a message accordingly
Added WOFS + other stuff

This should really be more than one commit, but I wrote everything in one
shot and I don't feel like arranging the changes logically into different
commits. So, these are the changes:

- added WOFS (Write Once File System). This is a writeable file system that
  exists in the MCU's internal Flash memory and allows files to be written,
  but only once, in a single shot. More details to follow.
- the platform interface has a new MCU flash access interface.
- added WOFS "reference implementations" for two CPUs: LM3S8962 and
  STM32F103RE. They are easily extendable to other CPUs in the same platform
  and can be taken as a model for other platforms.
- the ROMFS file layout in memory was slightly changed.
- the simulator (src/platform/sim) got a new function (lseek).
- shell: now each shell command receives its arguments in a C-main-style
  (argc, argv) pair. This was originally Marcelo's idea and it finally
  made it to the master (although this particular implementation is mine),
  after I got fed up with all the argument parsing in the shell functions.
- new shell command: wofmt ("formats" a WOFS, effectively clearing it).
- a couple of small fixes in the shell code
Fixed WOFS compilation on sim (Linux)
WOFS fix: at most one file opened in write mode

Due to the nature of WOFS, at most one file can be opened on WOFS
in write mode at any given time.
fixed check for remaining size on WOFS
renamed INTERNAL_FLASH_BLK_SIZE to INTERNAL_FLASH_UNIT_SIZE
fixed compilation when BUILD_WOFS is not defined
WOFS documentation, part I
WOFS documentation, part II + a small style change
WOFS documentation, last part + another style change
added board EK-LM3S9D92 from TI (LM3S9D92)
Use canonical Mizar32 web page URL
Bumped CPU frequency to 80MHz for LM3S9B92/LM3S9D92
Merge branch 'master' of github.com:elua/elua