(Issue #21) Increase Supported Memory to 256MB

[MisutaaAsriel]

Satisfying #21, utilizing the help of code from DOSBOX-SVN, thanks to a helpful VOGONS post, these changes allow the expanded memory to be increased up to 256MB.

Tested on an iPad Air 4 running iOS 15.

iDOS, with memsize=128, reports 128MB of expanded memory, with BOOTed systems reporting identically 128MB of RAM.

iDOS, with memsize=256, reports 256MB of expanded memory, with BOOTed systems reporting a total of 248MB of RAM. (Note: Unsure of why the discrepancy here, but when set to a lower value, DOSBOX & BOOTed systems match.).

iDOS, with memsize=256, reports 255MB of expanded memory, with BOOTed systems reporting identically 255MB of RAM. Previous statement was erroneous, due to a misconfiguration of a system file. Behavior is similar to that of 64MB versions of iDOS, which will report a total of 63MB available when memsize is >= 64, and is to be expected.

[litchie]

Thanks for your work. Will do some tests on it first. I think it may be useful for people running windows. However, I don't believe that we need to provide extra expand memory. Who are going to use it?

[MisutaaAsriel]

It's useful when running multitasking operating systems, such as Windows, so there is some benefit to increasing the expanded memory. — For those using purely DOS software, however, there may be little benefit.

However, having the option to use greater than 64MB expanded memory seems harmless, even if it only serves a subset of users.