FMSLogo Code

Use wxID_OK, instead of inventing my own ID for the OK button. I'm not sure what effect this has on FMSLogo, but it seems like the right thing to do.

Integrate updates to the Greek translation from Theodoros Chatzigiannakis.

Update test log based on 6.21.0 full test pass.

Update the Greek manual. I'm not sure why this changed, but it doesn't really matter, since we just use the English manual, anyway.

Bump the version to 6.21.0 for the next formal release.

Copy the updates for 6.21.0 into the changelog for the upcoming release.

Implement request #1377915; FMSLogo manual is now consistent in how it uses terms like "command", "instruction", and "item".

Insert a paragraph break to improve readability.

Add a definition for the term "element".

This is part of feature request #1377915, a manual that is 100% consistent in its usage of terms.

Replace some incorrect usages of the word "command" with something that is correct.

This is part of feature request #1377915, a manual that is 100% consistent in its usage of terms.