Fix Issue #83 - Panic on write without filename

See merge request !87

Adding in support for arrow keys in normal mode for moving.

Remove extra parenthesis around function argument to compile

* Compiling on 1.25.0-nightly fails due to extra parenthesis around
  function arguments
  * Remove to restore successful compilation

infer file to save to from file opened

Make buffers behave more consistent

Add bd command to delete a buffer.

Fix bug when entering invalid command in prompt

The history can be accessed using the arrow keys.

Fix bug that could cause panic when deleting lines

Add line numbers, wraps lines that are too long

Completely rewrote the io/graphics.rs redraw function.

Fix freeze on resize screen, impl tab as 4 spaces

Also fixes a bug when pressing 'L' on an empty line.

Vertical scrolling & rustfmt changes

Completely prevents the cursor from walking offscreen.
Also fixes several crashes when pressing 'z'. I still don't
understand how those are supposed to work anyway, but allowing
the cursor to go offscreen is never a good idea.

Implement 'I', 'A' and 'c' commands.

Also fixes a bug where pressing 'L' would put
the cursor beyond the last character of the line.

Fix a panic when using 'dL' or 'dG'

Fix Sodum logo in README

Seems like the path to the Sodium logo changed.

Fix a bug in insert_line

Assuming that insert_line(n) shall insert the string
into nth-line (0 based).
- Fix a bug in insert_line when insert into after buffer
- Do corresponding changes in other place

Add exit key

Fix compilation errors on the generic branch

Fix a panic when doing 0g

Fix the crash when deleting a cursor

Update README.md

The new behaviour is to go to the end of the document (as with vim)