Update documentation and CHANGELOG

docs/api/easyflash-programming-guide.md

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+[< back to index](../doc_index.md)
+
+### A note about EasyFlash
+
+The `c64_ef_small` target defines a 128 kB Easyflash cartridge image, with 72 kB effective ROM space.
+The program is run directly from ROM;
+typical ROM programming guidelines apply, see [the ROM vs RAM guide](./rom-vs-ram.md).
+
+The LOROM segment ($8000-$9FFF) is fixed and is the main code segment.
+
+The HIROM segment ($A000-$BFFF) is banked (banks numbered from `hirom0` to `hirom7`).
+
+Initially, the `hirom0` bank is banked in.
+It contains the initialization code, the initial values for RAM, and the EAPI (if used).
+
+You can switch the bank using the `switch_hirom(0..7)` function.
+
+In order to use EAPI, you need to include the binary distribution of EAPI at $B800 in `hirom0`, e.g.:
+
+    segment (hirom0) __eapi @ $B800 = file("eapi-am29f040-10")
+
+and call `eapi_init()`. It sets the `errno` value.
+The EAPI requires 768 bytes of RAM.
+You can choose the location of EAPI by defining the `EAPI_ADDR` feature,
+it should point to a page-aligned address in RAM, $200 or more.
+
+If you want to reinitialize the EAPI without copying it from ROM again, you can call `eapi_init_again()` instead.