complete previously-writen-to-file inline maths elsewhere

## completion examples:

type in line maths: ``` $hello$```,  ```\(world\) ```
then write to file, ``` :up```

### Single line:
to obtain:
```
$hello$  

\(hello\)

\[hello\]
```
using
```
$ [part-of-hello] C-x C-o

\( [part-of-hello] C-x C-o

\[ [part-of-hello] C-x C-o
```

### Single line, after other math
to obtain:
```
\( hello, world

\[ hello, world
```
using
```
\( hello, $ [part-of-world] C-x C-o

\[ hello, $ [part-of-world] C-x C-o
```
### Cross lines
to obtain
```
\(
hello, world

\[ 
hello, world

\begin{eq-env}
hello, world
```
using
```
\(
hello, $ [part-of-world] C-x C-o

\[
hello, $ [part-of-world] C-x C-o

\begin{eq-env}
hello, $ [part-of-world] C-x C-o
```

## ATTENTION:
1. If you want to write cross lines inline-math, use ```\( ... \)```, don't use ```$```:
```
$
hello $ [part-of-world] C-x C-o
```
gives:
```
$
hello $world$
```

2. Do not try to compete in line math on the right of ``` \begin{eq-env}``` in the same line.
It does not work properly if ```[part-of-eq]``` does not begins with ```\```
```\begin{eq-env} hello, $ [part-of-world] C-x C-o```

3. Even the following suggests nothing to complete:
```
\begin{env}  C-x C-o
```
Because ```LatexBox_Complete``` function always tries to find ```\``` or ```{``` on the left of current cursor position,
and then try to give a ```begin``` completion first.