fixed _sys_read()/_sys_write() issues.

finsh: fix finsh device setting

It is a big patch for stm32f0x, see the fellow :

1. rt_console_get_device should be call to set shell device only when it is null, or it will make finsh_set_device useless.
2. RT_USING_CONSOLE can be disabled in bsp/rtconfig.h

Cortex r4

Unit of "byte" is more intuitive than "long".

As the svc stack is the stack of threads, there is no need to allocate a
separate stack for the startup. Reuse the IRQ stack should be OK.

Tested on rm48 board.

    1. fix heap management for stm32f0xx(SRAM=8k)
    2. add USART1, USART2 driver for stm32f051R8
    3. fix finsh support for stm32f0x
    4. fix board components initial for stm32f0x and open debug msg
    5. add led driver(pc9) and test thread for stm32f0discovery board
    6. add init thread for stm32f0x do components initial
    7. add rcc initial for stm32f0x in rt_hw_board_init()
    8. add print rcc freq information function

the console output example is:
    SYSCLK_Frequency is 48000000HZ
    PCLK_Frequency is 48000000HZ
    HCLK_Frequency is 48000000HZ
    CECCLK_Frequency is 32786HZ
    ADCCLK_Frequency is 14000000HZ
    USART1CLK_Frequency is 48000000HZ
    I2C1CLK_Frequency is 8000000HZ
    SystemCoreClock is 48000000HZ
    initialize rti_start:0 done

    \ | /
    - RT -     Thread Operating System
    / | \     1.2.0 build Nov 15 2013
    2006 - 2013 Copyright by rt-thread team
    do components intialization.
    initialize rti_board_end:0 done
    initialize rt_hw_led_init:32768 done
    initialize finsh_system_init:0 done
    finsh>>

freemodbus: fix eol

On Windows platform, please set `autocrlf = true` and on Linux, please
set `autocrlf = input`.

net: add freemodbus master and slave v1.6.0

Signed-off-by: armink <armink.ztl@gmail.com>

Signed-off-by: armink <armink.ztl@gmail.com>

Fix hardfault bug for gcc port

for 2013-02-20 aozima commmit "port for gcc", but the commit is
not tested,and the kernel is breakdown in context_gcc.S, the file
is a copy from cortex-m3,but not port for cortex-m0, so i complete
this port for aozima, test it in stm32f0discovery board ,
and it works fine.

simulatr: print error messages when RTT_RTGUI is invalid

Revert "serial: set the errno if and only if in thread context"

This reverts commit 07bd09fc.
The validation of the context is done with in `rt_set_errno`. So it's
safe to call it here.

Serial fix

The errno is associated with threads. It will crash the thread if we set
it in interrupt context.

Return early if the size is 0 as there is nothing to do.