Add more data types

[pioneerAlone]

I'm using this library, any suggestions for adding other data types, in principle don't want to change the current logic too much

[Gordon01]

Hi!

Hope it's still relevant.

The approach depends on the types of data you want to store:

1. Do you want to save space and have small values like uint8_t?
2. Do you need to handle values of arbitrary size?

There are few ways:

• Quick & dirty: use multiple entries for storing values bigger than uwlkv_value. This approach doesn't require changes to uWLKV itself, but it does introduce overhead by storing the uwlkv_key multiple times for a single logical entry.
• Add support for variable-sized entries in uWLKV. This would involve adding a type field to uwlkv_entry and updating uwlkv_read_entry(), uwlkv_write_entry(), and possibly other parts of map.c to handle reading and writing the number of bytes based on the entry type.

[Gordon01]

A key may be reduced by one bit to indicate a sized entry (much like an UTF-8):

• 0 means an entry contains only a uwlkv_value and is UWLKV_ENTRY_SIZE length (classic).
• 1 means the next byte is the amount of the extra space reserved for an entry in addition to UWLKV_ENTRY_SIZE

Thus for classic entries layous remains the same, only losing one bit of the key.

For the variable size case, we can only store the size in NVRAM first time and use it for subsequent entries to save space. It will likewise add the need to dynamically calculate the sufficiency of space in the backup area.