toml: updated readme
# TODO: Documentation
+## NULL keys
+The plugin supports null keys. They are represented as special string of value '!ELEKTRA_NULL!' in a toml file, since toml doesn't support empty assignments. Be aware that a string of that value (full string must match exactly) will always be translated into a null key.
+
## Requirements:
- The plugin needs Flex (TODO: min version) and Bison (TODO: min version).
- Comments and newlines between the last array element and closing brackets are discarded.
- Trailing commas in arrays and inline tables are discarded
- - Comments/newlines between the last element of an array and the closing bracket are discarded.
- - Currently, only spaces in front of comments are preserved.
+ - Only spaces in front of comments are preserved.
## Questions
- Don't know where/how exactly to store trailing array comments/newline info
* Can't associate those info to array top key in the way like file ending comments are preserved
* Maybe add own metakey (eg. epilogue/comment/#1)?
- - How to handle null keys? (See storage plugin tutorial)
- * TOML doesn't allow empty assignments (eg 'key = ')
- * So how should empty values be represented in a toml file?
## TODOs
- Document functions
- Maybe preserve spaces
- Before array values
- Before assignment/simple table header/table array header
- - Don't store origvalue, if transformed value is equal to untransformed value
- Maybe use date plugin
