ecm boot overlap

[ecm-pushbx]

Several boot loader improvements:

• Bug FAT32 boot loaders: With a (rounded) file size of 128 KiB, either the file data corrupts the FAT sector or vice versa #127 fixed, files up to 128 KiB rounded up size work now
• Load segment 0x60 to 0x200 fully supported
• Memory map comments fixed and updated
• SYS checks that it seems to patch the correct magic offsets
• Mark all magic offsets in SYS and the loader sources
• On magic offset mismatch the new offset is displayed by the NASM error message
• Create listing files with correct names, fixes bug Boot sector listing files not named correctly #97

[ecm-pushbx]

Not yet included:

• SYS should warn if /L is < 0x60 or > 0x200
• SYS could detect kernel file (already present if /BOOTONLY or to be copied else) and cluster size and warn if load might fail
• One of the FAT32 loaders doesn't contain a license header
• The FAT12/FAT16 read buffer address can be accessed with +imm8 addressing now, drop the "word" to optimise this (some magic offsets will change)
• Loaders should set up stack before relocating (magic offsets of the load segment will change)
• Fix comments referring to 640 KiB as a kernel file size limit, this is wrong because we unconditionally relocate to 1FE0h:7C00h (27A00h) so the 640 KiB limit is not relevant
• SYS could detect magic bytes by scanning for them rather than hardcoding magic offsets