Internal_pervasives: add Error and Or_error
Fastq: switch to Or_error for error handling
add Fastq.write function
Range: pure whitespace fix
Range: make now returns Or_error and clean up

Also remove total orders, stop using Order module, and remove to_pair
function. None are useful enough to justify adding to the API.
RSet.to_canonical: stop using Order module

It is more clear to define the order relation directly than to use an
extra abstraction.
Internal_pervasives: delete Order module

It is no longer used and not useful.
Pos: simplify interface
Lines: provide Future-based IO ops
{Async,Lwt}_internal_pervasives: remove

We shouldn’t need these.
travis: pin flow to master
Internal_pervasives: add Sequence module
Internal_pervasives: remove Parse sub-module

Contained only a single function, which was used by only one function
in Track. Moved function within Track module.
Internal_pervasives: simplify and rename

We now `open Core.Std` explicitly everywhere, and `open
Biocaml_internal_utils` when needed. This is easier to maintain as we
don’t have to keep up with changes to Core. Also it is safer; Core may
override or disable certain functions, which we might accidentally have
not included in our our manual list of functions to include.
Fastq: add ops to read/write directly from/to file
define new biocaml_ez library

This library has blocking calls and raises exceptions.
Range.union: improve return type
RSet: remove unused exception
improve use of Result

Don't open it in module scope, especially to avoid overriding
ok_exn. Now opening Result.Monad_infix locally where needed.

Delete output_ok, output_error, and output_result functions. They only
avoided use of extra parentheses, which is perhaps not a good enough
reason to create an extra abstraction.

Rename Result.while_ok to Result.List.mapi, which follows Async's
choice to define Deferred.Or_error.List.

Replace Result.{return, fail} with {Ok, Error}, respectively.
Phred_score: improve API

Use Or_error. Move exception-ful interface to Biocaml_ez. Uppercase
polymorphic variant constructors.