This module implements a [Bloom filter](https://en.wikipedia.org/wiki/Bloom_filter). This is a probabilistic data structure that is used to test for set membership. There are two operations -- `add` and `check` that allow
arbitrary strings to be added to the set or tested for set membership. Since this is a probabilistic data structure, the answer returned can be incorrect. However,
if the string *is* a member of the set, then the `check` operation will always return `true`.
## bloom.create()
Create a filter object.
#### Syntax
`bloom.create(elements, errorrate)`
#### Parameters
-`elements` The largest number of elements to be added to the filter.
-`errorrate` The error rate (the false positive rate). This is represented as `n` where the false positive rate is `1 / n`. This is the maximum rate of `check` returning true when the string is *not* in the set.
#### Returns
A `filter` object.
#### Example
```
filter = bloom.create(10000, 100) -- this will use around 11kB of memory
```
## filter:add()
Adds a string to the set and returns an indication of whether the string was already present.
#### Syntax
`filter:add(string)`
#### Parameters
-`string` The string to be added to the filter set.
#### Returns
`true` if the string was already present in the filter. `false` otherwise.
#### Example
```
if filter:add("apple") then
print ("Seen an apple before!")
else
print ("Noted that the first apple has been seen")
end
```
## filter:check()
Checks to see if a string is present in the filter set.
#### Syntax
`present = filter:check(string)`
#### Parameters
-`string` The string to be checked for membership in the set.
#### Returns
`true` if the string was already present in the filter. `false` otherwise.
#### Example
```
if filter:check("apple") then
print ("Seen an apple before!")
end
```
## filter:reset()
Empties the filter.
#### Syntax
`filter:reset()`
#### Returns
Nothing
#### Example
```
filter:reset()
```
## filter:info()
Get some status information on the filter.
#### Syntax
`bits, fns, occupancy, fprate = filter:info()`
#### Returns
-`bits` The number of bits in the filter.
-`fns` The number of hash functions in use.
-`occupancy` The number of bits set in the filter.
-`fprate` The approximate chance that the next `check` will return `true` when it should return `false`. This is represented as the inverse of the probability -- i.e. as the n in 1-in-n chance. This value is limited to 1,000,000.
