Zxbasic

===
* ! `DIM f% = <value>` was not working. Now it does.
* ! HEAP memory init routine slightly improved.
Also removed a possible bug of memory corruption reported
by Britlion. (Thanks)
* New memory scheme: Now variables and heap zone are moved
to the end of the memory (high area). This should make
easier to implement data bank switching on 128K machines.
It also allows to `SAVE` all data memory in a single block.
This is a feature to be implemented in near-future releases.
* ! Undeclared local variables caused a compiler error.
They should just compile (like global ones do).
* ! String variables used in string slices where sometimes
optimized (ignored).
* ! `ELSEIF` constructions were not being compiled correctly.

===
+ ! Fixed a bug for constant string slicing, so
`"0909"(A TO B)` now works. Thanks to Britlion.
+ ! Expanded grammar to allow something like `"0909"(f)`
or `"0909"()` which are also allowed in **Sinclair Basic**. Thanks to Britlion.
+ ! Using expressions like `"0909"(f)` (like above) might corrupt the
HEAP memory, leading to a program crash. Fixed. Thanks, Britlion :-)
+ ! Fixed a bug in typecast from signed integers to float which
sometimes overflowed leading to wrong results.

===
+ ! `%` suffix was being ignored. Fixed.
+ ! Global string variables were not optimized unless declared
with `$` suffix. Fixed.

===
+ ! `BOLD` and `ITALIC` could not be used as permanent attributes,
only as temporary ones. Now they are allowed as permanent too.
+ Some more syntax compatibility with **Sinclair BASIC**. Expressions
like `F$(5)` and `PRINT ;;;` are now allowed.
+ ! Single `PRINT` sentences were not working (they should print a
newline).
+ Minor grammar corrections.
+ ! Using a suffix like `$` in a function declaration was being
ignored. Now it's taken into account.
+ Added support for `PRINT ,` (thanks to Britlion and LCD for the
suggestions and bug detection)
* Fixed a potential optimization bug for `SHR` and `SHL`

===
+ ! Fixed many optimization bugs (almost five). Thanks to LCD
+ ! Fixed ChangeLog file
+ Internal refactored code (somewhat)

===
+ Added the `ELSEIF` construct to the `IF THEN ELSE` sentence
+ Added more optimizations in some jumps
+ Added the `USR` function (both for Strings and Floats)
+ Optimized some print string generated code (now it's smaller)