Use nom instead of pest for better performance and neat code.

Currently, Cell is a mod in lib_xch which aims to provide safe computing (computing without overflow)

I am going to separate it from lib_xch in order to provide Cell to other projects.

WIP, I will post the schedule for it soon.

Excepted behaviors:

Mg+O2=C+MgO => 2Mg+O2=C+2MgO

Current behaviors:

Mg+O2=C+MgO => NoAnswer

Steps to reproduce behaviors:

Just use API simply to reproduce it.

Actually, there is no issue.

Description:

The library will panic when equation is A+A=B like.
panic info:

thread 'main' panicked at 'index out of bounds: the len is 2 but the index is 2', /checkout/src/liballoc/vec.rs:1551:10
note: Run with `RUST_BACKTRACE=1` for a backtrace.

Other notes:

• A+A=A+B thread 'main' panicked at 'index out of bounds: the len is 2 but the index is 3', /checkout/src/liballoc/vec.rs:1551:10 note: Run with RUST_BACKTRACE=1for a backtrace.
• A+A=A+A+B thread 'main' panicked at 'index out of bounds: the len is 2 but the index is 5', /checkout/src/liballoc/vec.rs:1551:10 note: Run with RUST_BACKTRACE=1for a backtrace.

HIGH LEVEL