filechecker syntax v2

**THIS IS A PROPOSAL: DO NOT MERGE**

I'm hoping for comments on the JSON syntax, to make sure that it is easy to read and easy to write by hand. The current syntax does a good job at being self explanatory, and I don't want to lose that in the new syntax.

The current parameters syntax of the filechecker module is very compact, but suffers from a number of limitations.
```json
{
        "module": "filechecker",
        "parameters": {
            "/home/*/.ssh/*": {
                "regex": {
                    "private ssh key in homedir": [
                        "-----BEGIN RSA PRIVATE KEY-----"
                    ]
                }
            },
            "/etc/passwd": {
                "regex": {
                    "test the presence of some users": [
                        "^ulfr",
                        "^kang"
                    ]
                }
            }
        }
}
```
* To perform a search on multiple locations, the search block needs to be duplicated for each location.
* Indicators are very hard to point to, there's no indicator ID, which makes adding a condition of the type `ioc1 or ioc2` almost impossible
* The syntax has no room for options. We cannot add flag to specific the max depth of a search, or prevent the search from crossing file system types.

The proposed syntax below fixes these limitations, but at the cost of a slightly more verbose structure. The goal is to avoid storing information is JSON keys, because that makes the structure hard to parse. Instead, each search maps to a static structure that is easy to extend if needed.
```json
{
    "module": "filechecker",
    "parameters": {
        "searches": [
            {
                "name": "private ssh key in homedir",
                "alias": "pkeyhomedir",
                "paths": [
                    "/home/*/.ssh/*"
                ],
                "regexes": [
                    "-----BEGIN RSA PRIVATE KEY-----"
                ]
            },
            {
                "name": "test the presence of some users",
                "alias": "localuser",
                "paths": [
                    "/etc/passwd"
                ],
                "regexes": [
                    "^ulfr",
                    "^kang"
                ]
            },
            {
                "name": "verify that root uses a strong salted password",
                "alias": "strongrootpasswd",
                "paths": [
                    "/etc/shadow"
                ],
                "regexes": [
                    "^root:\\$(2(a|y)|5|6)\\$"
                ]
            },
            {
                "name": "flag if shadow uses md5 for root",
                "alias": "rootmd5",
                "paths": [
                    "/etc/shadow"
                ],
                "regexes": [
                    "^root:\\$1\\$"
                ]
            },
            {
                "name": "look into /etc/ only, no recursive walk down the path",
                "alias": "etcnorecursive",
                "paths": [
                    "/etc/"
                ],
                "regexes": [
                    "^something interesting$"
                ],
                "options": {
                    "maxdepth": 0
                }
            },
            {
                "name": "look into /etc/ and all subsequent directories",
                "alias": "etcrecursive",
                "paths": [
                    "/etc/"
                ],
                "regexes": [
                    "$another interesting thing$"
                ],
                "options": {
                    "maxdepth": -1,
                    "crossfs": false
                }
            },
            {
                "name": "detect known dangerous binaries",
                "alias": "dangerousbin",
                "paths": [
                    "/bin/*",
                    "/sbin/*",
                    "/usr/bin/*",
                    "/usr/sbin/*",
                    "/opt/*"
                ],
                "sha256": [
                    "1e2699ff1f9238c58390c1ada53f4f21032ca5e0946bfb54a5a144452e6efc82",
                    "286c39ec3d8e4f15f353dca350ca7575e0269dba808206f3ce8d1a3ea142b353"
                ]
            }
        ],
        "condition": "pkeyhomedir or !localuser or !strongrootpasswd or rootmd5 or dangerousbin"
    }
}
```
This syntax should map to the following Go struct in the filechecker module:
```Go
  type Parameters struct {
          Searches  []search `json:"searches,omitempty"`
          Condition string   `json:"condition,omitempty"`
  }
  type search struct {
          Name     string   `json:"name"`
          Alias    string   `json:"alias"`
          Paths     []string `json:"paths"`
          Regexes    []string `json:"regexes,omitempty"`
          Filenames []string `json:"filenames,omitempty"`
          MD5      []string `json:"md5,omitempty"`
          SHA1     []string `json:"sha1,omitempty"`
          SHA256   []string `json:"sha256,omitempty"`
          SHA384   []string `json:"sha384,omitempty"`
          SHA512   []string `json:"sha512,omitempty"`
          SHA3_224 []string `json:"sha3_224,omitempty"`
          SHA3_256 []string `json:"sha3_256,omitempty"`
          SHA3_384 []string `json:"sha3_384,omitempty"`
          SHA3_512 []string `json:"sha3_512,omitempty"`
          Options  options  `json:"options,omitempty"`
  }
  type options struct {
          MaxDepth float64 `json:"maxdepth,omitempty"`
          CrossFS  bool    `json:"crossfs,omitempty"`
  }
```