Copied from https://github.com/LaurentMazare/ocaml-torch/tree/a6499811f40282a071179d4306afbbb6023dcc4a/src/gen/gen.ml

Also updated dune-project accordingly.

…a torch wrapper

Copied from https://github.com/LaurentMazare/ocaml-torch/tree/a6499811f40282a071179d4306afbbb6023dcc4a/src/wrapper

A. Non-void, non-* methods.

Search/replace:

1. torch_api.h: ^(?!void)(\w+) (at.+)\( -> int $2($1 *,
2. torch_api.h: , \);$ -> );
3. torch_api.cpp: ^(?!void)(\w+) (at.+)\( -> int $2($1 *out__,
4. torch_api.cpp: , \) \{$ -> ) {

B. void-methods.

Search/replace

1. torch_api.{h,cpp}: ^void (at.+)\( -> int $1(

C. *-methods.

Search/replace
1. torch.api.h: ^(\w+ \*)(at.+)\( -> int $2($1*,
2. torch_api.cpp: ^(\w+ \*)(at.+)\( -> int $2($1*out__,

D. Implemented return status code

Replaced
```
^(\s*)  return new (.+)
\s*\)
\s*return nullptr;
```
with
```
$1  out__[0] = new $2
$1  return 0;
$1)
$1return 1;
```

E. Implemented return status code

1. Replaced
```
^(\s*)PROTECT\(return new (.+)\)
\s*return nullptr;
```
with
```
$1PROTECT(
$1  out__[0] = new $2
$1  return 0;
$1)
$1return 1;
```

F. Implemented return status code

1. Replaced
```
^(\s*)PROTECT\(return (.+)\)
```
with
```
$1PROTECT(
$1  out__[0] = $2
$1  return 0;
$1)
```

G. Implemented return status code

1. Replaced
```
^(\s*)  return (.+)
\s*\)
\s*return nullptr;
```
with
```
$1  out__[0] = $2
$1  return 0;
$1)
$1return 1;
```

H. Restored error handling

Handled caml_failwith by search/replace: Replaced:
```
$
^(\s*)  caml_failwith\((.+)
```
with:
```
 {
$1  myerr = strdup($2
$1  return 1;
$1}
```

I. Replaced
```
^(\s+)PROTECT\(
    return (.+)
  \)
```
with
```
$1PROTECT(
$1  out__[0] = $2
$1  return 0;
$1)
```

J. Manual implement return status code

K. Changed return code from -1 to 1 to reduce diff

L. Fixed a couple of warnings

Also, made CUDA build optional.

int at_empty_cache();
int at_no_grad(int flag);
int at_sync();
int at_from_blob(tensor *, void *data, int64_t *dims, int ndims, int64_t *strides, int nstrides, int dev);

Also:
* Dev. container: Updated for Torch 1.10.2
* Added /build to .gitignore

Factored out scripts - for re-use in CI and dev. container.