A few documentation fixes

I've documented what is new in v6.0.0, in both the LibreOffice documentation and the comments in JavaScript.

The emulator now displays a call stack

The emulator now displays a call stack, the previous values of the program counter (the PC register) stored before executing the call command.

Refactoring and documentation fixes

I've added the db_helper.php file into which I extracted the code that's common to both db.php and deleteTheProgram.php files. I've also modified the documentation a bit.

Restored the compatibility with Firefox 52

The changes I made to viewer.js in v5.9.0 were, apparently, incompatible with Firefox 52. So, I fixed that bug in this release.

Made a few not tested adjustments to the PHP code

I've made a few adjustments to the PHP code. The PHP code does not contain syntax errors, but I was not able to test whether it works, because I failed to connect it to the MySQL database.

Better error messages and documentation

I've improved some error messages and I've improved the documentation a bit (mentioning the problems with cookies that occur in the Dolphin Browser).

Various documentation fixes

I've documented what's new in v5.8.0.

Made an x86 assembly version of the Binary to Decimal program

I've written a version of the bin2dec.psm program in a combination of 64-bit x86 assembly and C++, and named it bin2dec.cpp.

Fixed another important bug in the parser regarding unary operators

The statement inst --5 now parses correctly as inst 5, rather than crashing the parser.

Fixed an important bug in the parser regarding unary operators

I've fixed the issue #42 .