Migrating to version 3

Version 3.0 introduced many relevant new features, mainly on-hardware running/debugging. Most changes in the IEC 61131-3 languages are backward compatible. Device implementers will probably need to make some changes.

Changes in IEC 61131-3 languages

STRING declarations now accept a size specification (from 1 to 255). Eg:
```
     S:  STRING[6];
```
If not specified, it defaults to 80. Assigments that exceed the allocated size are accepted - they are silently truncated
Function calling:
- VAR_INOUT now behave as they should: they are passed by reference, hence they can be modified inside body.
  VAR_INOUT arguments cannot be ommited in function calls
- Function calls cannot ommit INPUT arguments (except for extensible arguments and EN).
- EN/ENO: they are true variables only for FB (Function blocks). For functions, they are resolved at call time, they cannot be accessed inside the pou body.
- Nonformal calls in textual languages are accepted only for functions (not for FB)
- Previously we accepted the function output name as an OUTPUT variable that could be mapped in formal calls :eg: ABS_INT( IN := 3 , ABS_INT => ret) This is prohibited now.
INPUT variables cannot be modified inside POU body (as per spec)
INPUT/OUTPUT variables in Functions cannot be assigned INIT expressions
Graphical languages: the internal logic of blocks execution and storing of intermediate values has changed (briefly: each "link group" is assigned a storage value that can be a connected variable reference, or a FB terminal input/output or, as last resort, an additional hidden variable; a wired-or has always a hidden variable).
Graphical languages:Feedback connections are prohibited when they go back to a wired-or link group.
VAR_INOUT in Graphical editor: they are displayed with a & prefix, only on the left (input) side of the blocks

Miscellaneous

Workspaces from previous versions should work, but it's nevertheless recommended to use a new clean Workspace, and import (with copying) the existing projects
When using for first time IDE version 3 it will always be needed to input the user license.
Changes in included devices. In Windows, the old DEFAULT and SAMPLEMODBUS devices are now WIN_LOCAL and WIN_WITH_MODBUS, and both are placed inside directory devices/win_local. Also, two new sample remote devices are included: linux_ssh, linux_tcp; both are place inside directory devices/linux_remote.
Java 8 is required now. The GEB IDE for Windows no longer includes a JRE, if your Windows machine does not include a Java 8 (32 bits) version, you should install one from https://www.java.com/en/download/.

Device programming

Handling of IO variables (directly represented=AT vars) has experienced some changes. See details at "OEM tasks" documentation.
Device configuration file has a new more powerful syntax to accomodate on-hardware running/debugging. See the configuration files in the include devices (eg. c:\geb3\devices\win_local\device.properties) for examples and documentation.
Binary entry point (main) : if you want your device to support on-hardware remote run/debugging, the program should process some predetermined arguments. See in common_f.c the sample implementation and documentation of function
```
static bool parseArgs(int argc,char **argv) { 
... 
}
```
Also, it's recommended to follow the convention regarding return codes: (0=ok)
Main loop: "hooks": the expected behaviour of the main execution loops now includes calling the hook function at the appropiate times:
```
void geb_hook(int where,bool debugmode)
```
The device implementer should include this calling in the loop (and on starting and ending), and the geb_hook function itself. Use gebLoop() and geb_hook(int where,bool debugmode) in common_f.c as templates.
On hardware debugging: Low level communication. For the device to support on-hardware debugging, it should provide its own low-level communication stack, implementing in debugcomm.c the functions defined in debugcomm.h. The implementation provided in the sample devices should be ok for environments that support sockets (Linux and Windows included).
IEC custom Libraries: for now (version 3.0), support for custom libraries is disabled. Only "external libraries" (pure ST code) are supported. This is expected to change in future versions.