introduce idris-core.el, on which all .el files depend. this loads idris-compat

this was suggested by @purcell and should solve issue #25
Adapt behaviour of C-c C-t to the same as the other interactive commands:
- save buffer
- load file synchronously
- send command over the wire to Idris process

Additionally, provide a prefix option for C-c C-t which does not load anything, but rather asks for the thing to check
Provide prefix argument to load which does not pop to the REPL buffer
fixes #27
Add initial Commentary section to idris-mode.el

RE issue #26
fix typo
use apply-partially instead of a lexical-let
Support yasnippet

Idris-mode now dynamically generates yasnippet snippets from the code
bits that it receives from the compiler, enabling tabbing between the
fields that need filling.
insert output at right place (after prompt), always insert a prompt after a command
fixes #13
Add README info and demo for interactive editing
Ensure that both Idris process and the idris repl buffer is up and running,
before calling Check.

This was not the case for C-u C-c C-t... now there is a common entry point which reduces code duplication
add documentation for prefix arguments and C-cC-l
Stopped idris-load-file from unconditionally erroring
Replaced key specifiers like [return] with ?\ escapes.

For some specifiers, I was either unable to test them or could not find a
suitable replacement. These have been left alone and still don't work for me.
Changing "\t" to [?\t] for consistency
Merge pull request #31 from trillioneyes/fix-keymap-declarations

Fix keymap declarations
support for a :warning format with either line number, or line number and column (#731 in idris-dev adds the column)
delete all overlays if idris is quit; fixes #32
include note about idris version (to remove once a future idris release is out)
Add dirtiness tracking for Idris mode

Now only reload files when they've changed since the last time they were
loaded. This makes C-c C-t useful on large files.

The loaded status is shown on the mode line to make any delays predictable.
Changed all keymap definitions to use kbd instead of escapes