Demonstrate command and print procedures usage in sqscripter-test

Invoked command procedure echoes back the command (it desn't interpret the
command), and shows a message box to show the entered command.
Get rid of multi-byte characters in VC2012 project filter file
Change interface to allow multiple instances of ScripterWindow

The API is made C compatible by extern "C" linkage and absent of C++
structs or classes (only PODs).  This would make many other native
compiler languages also be compatible with the API.

Also, source file open dialog's filter can be customized by the caller.
Fix File->Open menu fails to load a text file but first character

SetWindowTextA() actually converts the given text to Unicode prior to
passing to the message procedure.  Scintilla control assumes that the
passed string is ASCII (or multibyte string in C language's terminology),
so it finds the second byte of input string as string termination (NUL
byte).

SendMessageA() with SCI_SETTEXT resolves this issue, although I still
don't understand why.

Note that the Scripter source depends on Scintilla header file from now
on.
Fix screwed up project and source files for x64 builds

The compiler for x64 complains that GWL_USERDATA is not defined.
We must use GWLP_USERDATA for portable source.
Add a interface function to execute a loaded source buffer

Test program demonstrates Run button effect by showing a message box
followed by file content dump into the output buffer.  The test program
has no script executing environment whatsoever, so it only shows the
loaded content, but it could be arbitrary scripting language which
can be interpreted by the application.
Move Sqscripter sources to SciLexer.DLL project itself

We have to define a custom dialog box with separate resource script
from host application.  This is most easily done by embedding the
dialog template resources to SciLexer.DLL itself.
Get rid of warnings in x64 build in sqscripter.cpp
Add 'sqscripter/' from commit '1ce84297ed92aa774c43400d37358f07953ba0f8'

git-subtree-dir: sqscripter
git-subtree-mainline: 6fce98b53ea5b7f326b92442b5fbbfd258a376aa
git-subtree-split: 1ce84297ed92aa774c43400d37358f07953ba0f8
Adapt to sqscripter project (modified SciLexer.DLL)