Pulled out word functions
Word extraction from a list
* and # for current-word searching
word-list code - needs merge from feature/cmd
Basic parenthesis matching
Initialise ui_paren with { -1, -1 }
Dependency update
Pull out replace-curbuf code
Basic jump-to-tag word function - ^]

Needs work to handle full ctags output properly.
Made errors more obvious - background red
buffer_current_line() takes a "create" argument
Fix crash when reading into non-existent lines
:r sets the modified flag
Change k_docmd() structure to support argv or arg1 functions
Prevent io-mapping when part-way through a key sequence
Add \x binding for reading from an external command
Use the list_new_fd / fast mmap file reading
mmap_new_line() sets len_{malloc,line} correctly
mmap_new_line() doesn't leave an extra line
Use != for mmap_to_lines() iteration