Replace use of Any by an enum

[pcpthm]

Fixes #17.
I came from hacktoberfest tag and not familiar with the codebase so I kept in mind to make minimal changes.

[Empty2k12]

Looking good. Documentation can be improved for the enum, so users of this library know what it's doing.

[Empty2k12]

Please add some rustdoc comments so it's clear what this is used for for users of this library.

[Empty2k12]

LGTM! Thank you for this contribution. Happy hacking for Hacktoberfest.

[Drevoed]

Was this merge and Pull Request really necessary? We don't have to store references to read/write queries and more importantly, influxdb-rust already had QueryType. Code using Any could be refactored without the addition of redundant enums. Trait InfluxDbQuery describes a method get_type which returns either QueryType::Read/WriteQuery depending on a struct.

[Drevoed]

@Empty2k12

    pub async fn query<Q>(&self, q: &Q) -> Result<String, InfluxDbError>
    where
        Q: InfluxDbQuery
    {
        let query = match q.build() {
            Err(err) => {
                let error = InfluxDbError::InvalidQueryError {
                    error: format!("{}", err),
                };
                return Err(error);
            }
            Ok(query) => query,
        };

        let basic_parameters: Vec<(String, String)> = self.into();

        let client = match q.get_type() {
            QueryType::ReadQuery =>
//...

this is how it could and should (imho) be done (why add something to the crate when we already have it) and is how I'm implementing an async-await unstable feature right now

[pcpthm]

@Drevoed If I can break API, my opinion is:

• InfluxDbQuery trait is unfit because it is not semantically open (it has to be either read or write query, no consuming crate should be implement this trait). It is currently also used for something like a something like a module but is is wrong. Remove it.
• New InfluxDbQueryTypes can be used only for the purpose of "overloading" emulation. Not necessary TBH.

[Drevoed]

@pcpthm I agree and I've come up with a different solution then, seeing as crate is still in 0.0.* and allows breaking changes. Something along the lines of this:

pub enum InfluxDbQuery {
    Write(InfluxDbWriteQuery),
    Read(InfluxDbReadQuery)
}

impl InfluxDbQuery {
    pub fn build(&self) -> Result<ValidQuery, InfluxDbError> {
        use InfluxDbQuery::*;
        
        match self {
            Write(write_query) => write_query.build(),
            Read(read_query) => read_query.build()
        }
    }
}

this follows your idea of removing an InfluxDbQuery

[Empty2k12]

I'm happy to discuss a more semantic API for this crate. Usability and code readability for implementers should be highest concern. I had no one to check the semantics of the API I designed, so I'm thankful for all feedback.